No one can grab onto the collective, so it's not at risk in that way. Their bodies are, in turn, replaceable and expendable. Perfection, in fact, is disembodiment, according to the queen.
so why do they still keep the bodies? assimilate the info and discard the body. they could use the bodies as fuel. they could all live as one consciousness within their systems. are drones even necessary with all that tech? can't they just deliver the nanites via raining them on the planet? transporting them in the ships? drones seem more like a liability for the collective as people find ways to get at the collective through drones.