For some reason, on my test site, the payment went through, but the site didn't actually renew. In fact, the account lapsed and went to free.
I noticed this morning that for no explicable reason, my Pro Sites settings had all reset. This is scary for me, because it would completely break the functioning of the site. I don't understand why the settings themselves would ever be volatile. All I did was install the multi-domains plugin, and it seems to have nuked pro sites completely.