Can u get it after u join the stormcloaks and attack whiterun ?

Yes. Jarl Baalgruuf is in the basemant of the Blue Palace in Solitude.

Yes. You still get the quest from the hotel lady, you just have to go to Solitude to talk to Balgruff.

Levanon! Ninja me, will you? bliviongate:

I believe you still can as it hasn't disappeared from my journal. I haven't bothered to do it because it's the worst quest in the game.