Giving them a bit more time is certainly fine and I hope that last person contributing here is okay.
Based on what has been said it seems like they might be in crisis. I sold some personalized items on Etsy in the past where a customer was super communicative up until they suddenly weren't. Often it was due to them, or one of their family members, suddenly getting sick or having a serious accident. Or worse, someone died.
Bad things often happen. We will try to be patient and understanding, and helpful where possible.
If the final holdout cannot be reached and they are unable to participate then they can eventually be cut from the bundle. I bet there are tutorials on how to make that work on the itch Discord, or maybe it is discussed in a tutorial somewhere else online like on YouTube, some itch related blog, etc.
And if Pixonix can't figure out how to do that, well:
I am not thrilled by the option of starting the whole process over but if we do submissions again maybe I can have 2 or 3 asset packs submitted next time to assist and not just the one. It's a learning experience not just for the bundle creator but also for many of us as participants. I didn't realize multiple submissions were even an option going in. Now, seeing what others did, I do. Maybe a few additional new people can contribute added valuable content the second time too to fill this out more. I mean, in the event we do have to restart we might as well expand on things a little bit the second time to improve the odds of the bundle being effective when it finally launches. If nothing else, that allows us to recover the losses from the material which got pruned out.