I made a stronghold my house and I was wondering after 1.9 is fully released will boss mobs spawn in it? And if you defeat said boss mob does it respawn?
It is very possible that boss mobs or unique mobs will spawn in your Stronghold. However, it's also possible that you will have to find a new Stronghold to get these monsters. It all depends on the way that Notch/Jens implements them.
As for your second question, I'd imagine that a boss would not respawn after defeating it, though I can't say for sure. I guess we'll just have to wait and see.