I think everyone is overreacting,just because a few Devolopers(there is no official number) moved to other games does this not mean that the game is "dead" it still has his Community and its still going to get updates with more Heroes and new events.
The loss of developers sucks, but yeah, that's not that huge. As I've mentioned before, the problem is that they're removing all sponsored competitive play, which means that a) a lot of top players are abandoning HotS, and b) HotS will be lower visibility, which means less players and longer queue times. These are liable to compound on each other and send HotS into a death spiral. It won't be immediate, and there's a chance for things to change, but as it stands now HotS is on a dead-end road.