Do they really? I would think that any living Tyranids aren't redigested as that would be pretty energy inefficient so I think they just are brought back to the Hive Ship and made to hybernate until they arrive at the next planet.
Also I feel like that would be annoying for something like the Swarmlord, which has to remember all of the times that it's been redigested, spawned, redigested spawned, and possibly killed at some point as well. I feel like that would get annoying eventually.



Its just that 40k battles are small skirmishes compared to planetary conquest.
Darnok