I don't remember specific words but it was strongly implied if not outright stated that he was basically ready to play the last few games of the season. There was just no sense in playing him. I believe he was fully cleared for practices. I could be wrong about those specifics, but the bottom line is he seemed to be healthy at the end of the season, so he should be perfectly fine when camp rolls around.
The questions with him are:
Is he mentally over it? Ennis plays in traffic with a lot of heart and grit. Will he be able to get right back to that?
What happens if he gets another concussion? His career could be in real jeopardy if it isn't already.
Can he actually take a step forward? He had a very strong 2014-2015. His totals would've been higher if the team wasn't utter garbage. He followed that up with a strong World Championship. When 2015-2016 rolled around, he looked like he really regressed to trying to do too much with the puck, something that's been an on again, off again problem his whole career, then he got injured. Granted, the whole team struggled to start last season, but he doesn't really have a place on the team if he's going to play like that. If he can bring his best game, the team will have a strong scoring depth.