Dawn would've still opened the portal which would mean that Buffy would have still jumped and killed herself, rather than letting Dawn sacrificing herself.
With this in mind, I'm pretty sure that Glory would hunt down Dawn again and re-open the portal. That's what she had on her mind throughout the whole of Season 5, it was her determination, so I think she would attempt to re-open it. I don't necessarily think that she would try and humanity; at times it seemed that she thought she was above humans, so I don't think she'd get much pleasure from that.
However, saying that, I believe that she'd get revenge on the Scoobies as she'd track down Dawn again. They stopped her first attempt, she definitely doesn't want her second attempt ruined and the fact that they've made her stay in our world for longer than necessary. And she'd have more of an advantage without the Slayer around. Yes, Willow and Tara are powerful witches but I don't think they'd be a match for Glory, nor Spike for that matter, as we saw in Blood Ties. I think Willow and Tara could slow her down but at the end of the day I think Glory would've gotten her revenge as well as getting back to her own dimension.