After units die there should be husks left behind ( like in supcom ) were they can be reclaim for a certain % of there original resource higher tier units have more reclaim value would make PVP maps have another layer to them. As you could make maps that have high reclaim units in the center or in POI's that make early game more interesting.
That would be a huuuuuuge mistake. As someone who plays competitively on evict semi-regularly, the game already has huuuuge snowball potential.
A simple way to make the game less defensively oriented would be to make unit cap depend on number of factories instead of cores. Your proposed change would make placing turrets an easy way to lose.
It's a good idea... just not for this game