He will gain his grand slam next season. This season he only needs to prove he can beat Barca and maybe bag the champions league.
If he goes out at semi-final stage of CL and doesn't win the league, he's gone. I get the sense that the people upstairs in Madrid don't really enjoy Jose's personality or presence anyway and won't tolerate if he fails to deliver this season. I don't know why people try to apply normal logic to decisions taken by the Real Madrid board. They never, ever show it, so firing Mourinho after his first season if he doesn't secure the honours is exactly something they're almost guaranteed to do, I think.