What animal can we not live without?

[CalMeacham]

Duck-Billed Platypuses. Trust me on this.

[FormerMarineGuy]

@CalMeacham

Duck-Billed Platypuses. Trust me on this.

Those things scare me.

[Mangetout]

@Blake

That’s a huge group you’ve just named. Almost every insect group I can think of has numeorus carrion feeding members: wasps, flies, beetles, moths, bugs, crickets and so forth. I hardly think that naming an entire functional group is in the spirit of the OP. We might just as well name “all bees and other pollinating insects” or “all plankton eating vertebrates”.

I know, but it’s the closest I could come to an answer.

The other question is how long it would actually take for scavenging mites, amphipods, worms birds and so forth to fill the niche. I doubt even the disappearance of such a broad group would have any noticable impact on most people.

I agree, and in fact this effect is why there is no candidate for the OP’s question. There is, AFAIK, no narrowly-definable group of animals that performs a function that is both unique and vital to human survival.