I'd be really disappointed and surprised if they added respawning enemies.
The game is meant to be somewhat difficult and therefore rewarding. In my opinion there absolutely HAS to be the possibility of failure. I want my choices to mean something and they won't mean anything if I can always trade time for XP and this game is about decisions not grinding. If you failed it means you made the wrong decisions.
Take the XCOM series, that series is pretty brutal and you can absolutely waste hours of gameplay and fail only to start the whole process over again, that is the punishment for failure in that game and I love it.
So if we accept that the game is designed to allow for a certain amount of failure and then you fail, how is it that the game is broken unless you falsely believed that you shouldn't be allowed to fail?
You SHOULD have to scrutinize all of your decisions in this game and agonize over where to put that extra point. You SHOULD have to come up with a viable plan to get enough XP to get over the next hurdle.
If I had to use one word to describe the game it would be "Rewarding". You don't get that feeling without some chance of failure and that level of reward directly correlates to that risk.
