This shouldn't have surprised anyone. He'd have been a fool not to opt out.
I think it's quite likely he isn't back.
If I'm Danny, I'd offer to overpay him on a 1-2 year deal (maybe 7-8 million per year) if he plans on bringing KG (and possibly Ray back). He's worth it with the Core Four. We absolutely cannot offer him more than two years, though.
However, Bass gets most of his offense off of open jumpers and dunks. He won't get that if he's featured in an offense, so we shouldn't pay him like that.
I also think Danny will look long and hard at JaJuan Johnson as a replacement for Bass. He was our first round pick, so he should be looked at to step in and play a role next year. Plus, like Bass, he can hit a jumper and finish around the rim.
Now we just need him to bulk up some.