I think Buffy formed a slayers council - which is like the watcher's council but with the important people at the centre and the watcher's working for them. Fortunately the old watcher's council kept all their gold in a separate building to their headquarters so it wasn't destroyed when Caleb blew up the council. Using a combination of witchcraft, watcher's gold and the personal libraries sent to them from retired watcher's, Buffy set up a new headquarters to train all the newly called slayers, though she left Giles in charge of the day to day running as she was in Rome, living her best life.
The headquarters acted as a training ground for older slayers and a school for younger ones (I know the comics pretend slayers don't come into their power until they're about 15 but we literally see a little girl get her slayer power in Chosen, so I am confident in saying the comics are incredibly wrong there, as their soft canon contradicts proper canon - and slayers can now be any age from new born to elderly - the hard canon of Dana, who is at least 25, in s5 proving slayers can be older than Buffy). Because there are so many of them, it is entirely up to the slayers whether they fulfil their duty or ignore it and get on with their own lives- but they have community and thanks to the watcher's gold, active slayers now get paid. (Buffy wanted to make sure no slayer ever ended up the way she did in s6)
Younger slayers go to slayer school as it would be dangerous to have super strong little girls in normal schools, but they receive a well rounded education and so once they are grownup, they can make a choice on whether to slay or enter the normal world. As the years pass by and there are more and more slayers across the world, they open up more and more headquarters so the girls can stay closer to home while they receive their training.
Buffy got a lot of satisfaction from setting the council up in her own image and making sure no girl was ever treated the way she was or suffered as she had again - but mostly, she's happy to be out there doing her slaying thing, money worry free and enjoys travelling and studying to keep her busy when she isn't averting apocalypses. After having the weight of the world on her shoulders, just knowing that there are other slayers out there gives her a huge sense of liberation and allows her to enjoy her calling.
Angel and his friends survived the night in the alley (except Wesley) but the senior partners continued to rain hell on earth down on them. They used Lindsey's tattoos to disappear and went out to seek a way to rebalance the scales and stop hell on earth (or at least L.A). Cordelia - as a higher power - guided them to what they needed in order to put things right. (side note, she and Doyle are together and blissfully happy).
Wesley was still bound by his contract and so was still working for Wolfram and Hart after his death. He was put down in their records room - where all actions on earth are recorded and his job was to record what Angel and his friends were up to. But of course the senior partners understand neither love nor free will and so - knowing that Angel was hidden by the tattoos and knowing the senior partners wanted to find him - Wesley made up a whole load of lies and recorded them in the book, so the senior partners would never find Angel. Once this was discovered he was severely punished and sentenced to eternal torment, but Cordelia rescued him and now he works as an ethereal servant of the PTB.
Both the PTB and the Senior Partners decided that Willow was becoming too powerful to remain on earth as a mortal. They both tried to recruit her to their own side - and she is now an immortal higher being playing her own game, with both sides thinking she works for them. She is actually responsible for Covid 19 - but that is a long story.
All these years later, Angel and his team run a slayer school out of the Hyperion. Angel teaches art and history, Spike teaches literature, Illyria/ Fred teaches all the science and maths, Lorne came back and teaches music and Gunn teaches law, lore and citizenship as well as demon languages . They cobble together Geography and woodwork but figure the girls can just google that if it ever comes up. Faith runs a similar school on the east coast. They have a friendly coast vs coast slayer rivalry.
Xander is married to Vi. Xander is a carpenter, Vi is a nurse. They have mostly retired from the demon slaying life but always return if Buffy needs them.
Oz and Nina are married. They live in Portland where she owns a little shop which sells her own ceramics. Oz is a session musician. He has taught her how to control her inner wolf come the full moon, though some months they don't bother and just let the fur fly.
Dawn left the slayer world behind to go to college and lived a normal life for a good long time. She went to Harvard and got a doctorate in international relations and started working for the diplomatic service. But it was at work where she met a young man by the name of Connor Reilly and they started to date, keeping many secrets from each other, until a random vampire attack and then the truth came out on both sides. When she turned 24 - after ten years on earth - she was dismayed to start developing powers, the key part of her was growing stronger. She can teleport and open gateways to different places, if she focuses her energy she can use it to kill things, the way it killed Buffy - but that takes a lot out of her and is only ever used as a last resort. As Connor was already a superhero living a normal life, she decided to be one too and stayed true to her career path. They are currently stationed in ... Kuala Lumpur, working for the American Embassy. They have two boys. Buffy is a doting Aunt and Angel is a delighted grandfather ... though they tend not to visit at the same time as it is all too majorly weird.
It was Spike who shanshued - eventually. Angel having signed away his right to it. It was a hard transition for them both; Angel realising he would be a vampire forever and Spike having to get used to not having superpowers any more. He stayed with the AI team for a while, and Gunn mentored him in demon hunting without the super strength.
Buffy was never told that Spike was alive after Chosen, never mind that he had shanshued.
In December, Buffy went to Kuala Lumpur to spend Christmas with Dawn (Dawn opened up a gateway to walk her through, other wise she would have been subject to the same lockdown rules as all of us). There was an unexpected apocalypse situation ( a real one - not a plague). They called in Vi and Xander to help out (Connor wanted to call Angel, but Buffy vetoed the idea) and together they started to work the problem.
But what they didn't know was that the threat was an old enemy of Illyria's and the team were already all over it. Cordelia had magicked them to Malaysia and they were already thwarting the apocalypse.
So both teams were doing their thing, there were a few near misses but they never quite managed to bump into each other - and on new years eve, at the stroke of midnight the demon was defeated, the threat was vanquished, the world was saved - and Dawn/ Connor and Xander/ Vi were swept up in their new year midnight kisses and Buffy was all alone. So being Buffy, she went off somewhere to mope for a few hours.
Meanwhile the AI team were packing up to leave.
Spike went back to the scene of the fight to retrieve his sword, just as the sun was beginning to rise.
Buffy was there - all alone - she heard a noise behind her and turned to look.
Just as Spike walked out into the sunshine...
It was just like the end of OMWF with the rising music and the rising ... music.
As far as I am aware, they have not yet emerged from their hotel room.
. I do think Not Fade Away suggests that Spike and Angel are dead. I guess the main thing I headcanon for all of them is that they have a nice balance between a normal life and supernatural life.
