at the end of one mission I was killed and was forced to restart - that's indeed very annoying. a save feature or some sort of "resurrect" feature could fix it.
Press T, that is a complete health restore (on a cooldown) and that should help you get through these quests easier.
As for not doing a quicksave, we have reasons for this. Now we do on the other hand, see some of our quests as needing changes and updates and this will be an ongoing process.