Okay, just spit balling here...
Since D&D has always been a combat heavy game, and the new edition makes it explicit that hit points are more than just meat on your bones, it consists of enerat, agility to avoid blows, and endurance. There are some complaints about lack of healing, and people not wanting to play healers (especially when they have to use their whole round just to heal). So... Why not solve all those in one mechanic?
Monster hit dice and levels come back. Most monsters are d8 like the old days, weaker monsters are d6, tougher monsters are d10, etc. This doesn't determine their hit points at the start of the fight, rather the amont of hit points you regain when you kill the beauty? You down a 1st-level d6 monster, you regain d6 hit points, in the form of being reinvigorated by the minor victory.
