It's a good question, and really, the crux of the whole issue. I don't have evidence, just belief... The value of incremental knowledge, and of lives lived without scarcity consciousness, when measured across large enough time-scale, could have exponential impact on humanity (snowball effect). Whereas the cost of UBI, while large, is relatively linear.

Hopefully, some of the experiments on UBI can start to provide the evidence.

I suppose what I'm asking is are there are enough resources to allow UBI right now with a major chunk of the labor force (and subsequently tax income) disappearing?

We're going to find out regardless, with large swaths of retirees leaving the labor force to join Social Security.