To the original post SMG is just saying politely in so many words that she has no interest in reprising the role of Buffy any longer. Joss isn't interested either, he has moved on to bigger and more exciting things, so this is all moot. It's in the past. Only a reboot is a possibility at this point, which I think most of us would agree. A reboot could definitely happen at some point in the future...but I personally don't think it is quite time for that yet.
This.
Interesting as it might be, I don't see the Buffyverse being able to succeed on the big screen even if everyone was onboard with the idea. Popular as Buffy and Angel still are, to do a single movie justice, it would likely be fairly expensive to make, and sadly I could easily see it doing rather poorly at the box office.
That and we've had 7 seasons of Buffy(I'm not counting comics personally) and 5 solid seasons of Angel, not counting Mr. Boreanaz being on the first three seasons of Buffy, counting his own show is actually the character that's been in the most episodes across both series.
Much as it would be nice to see them in character again, I can also understand the idea that none of them would want to necessarily end up typecasting themselves into the roles too much, or jumping into some poor quality spin off or whatever and tarnishing their past work.
If you're going to explore the Buffyverse via tv or Netflix with new material anytime in the next decade, pick someone like Faith or Willow say as a main character but otherwise bring in all new never before seen characters. We've seen Buffy and Sunnydale. We've seen Angel working for redemption. If the Buffyverse is explored in live action again, look for another avenue or aspect of the franchise to tap into.
I wouldn't necessarily be opposed to the idea of a hard reboot at some point, where everything from the original two shows is essentially tossed out the window and they pretty much start from scratch, but if they go that route, I'm hoping it's at least a decade or more in the future for something like that.
That being said, even if SMG or Mr. Boreanaz or Mr. Marsters or anyone else aren't willing or interested in reprising their original roles, if a future Buffyverse spinoff or hard reboot does come along, I would still talk to them as a courtesy. Even if they don't want a staring roll, it wouldn't be unheard of for someone to have a walk-on roll or play a bit part of some other extra or background character in a show, or maybe see if someone's interested in behind the scenes work or something.
If they did do some sort of spinoff such as a Willow or Faith or something, personally I think the best route to go would be a really short series/season similar to the recent Marvels: Agent Carter series, something only 8-10 episodes long per season. And make each season as self contained as possible. Leave a couple odd threads or something to open the possibility of additional seasons, but basically go in from the beginning anticipating a show not getting renewed.
