Sowers are included in the game, I think the terriforming roombas should be allowed to repair the damage caused by the cravers.  There could be an infinite building item that replaces exploitation.  It could even increase it beyond 100%, as one of the abilities.


Alternatively, if the green machines don't return, but you want them present in the game, then there could be a random event or quest triggered when you have a depleated planet where they can repair the damage.