Curious - in this situation, does delve return money to YC? Or YC simply writes off the investment

Neither. "Leaving YC" or "being removed from Y combinator" really just means you (more precisely, your YC/HN account) loses access to internal resources like bookface. This does have the knock on effect of essentially isolating you from the community. It's not entirely a punishment, it can be as simple as you are a person who isn't working on a YC company anymore, for example.

This has zero bearing on equity, which would be a different conversation. In this case, I think the YC SAFE is likely to remain as-is, unless the founders choose to return the money, or YC chooses to levy a heavier allegation of fraud (which they don't seem to have done here).

Ya it’s a total write down, I dunno how much they took from YC, if it was the standard deal this is just the cost of doing business.