The premise is flawed. It assumes humans required those species to continue (such that "humans die off" actually occurs). We very clearly did not require the ones that are already gone, and we clearly don't require these unknowns to continue forward either (if we did, we wouldn't exist, much less be thriving as we are).

In fact, it's almost guaranteed at this point that humanity has reached an instigation of self-controlled evolution take-over that can no longer be stopped or turned back, short of an extremely near-term (within a century or so) self-destruction event.

Within this century, humans will no longer exist as we think of the species today. There's no amount of extinction that is likely to occur in that time frame to prevent humanity from pushing radically forward in governing its own evolution. Where we're going, these 'natural medicinal opportunities' will not matter. The hyper evolutionary leap that has already begun with robotics, CRISPR, AI, etc., will make most of this discussion hilariously trivial very soon. There's nothing that likely can stop what's coming at this point (unless someone wants to load up an asteroid event soon).