I'm very, very grateful for all the kind thoughts. I won't be able to answer each one individually, but every one touched me.
My parents are fiercely independent. I booked a flight to leave tomorrow, but they insist they want a week to deal with things before family comes up, so I canceled it. Which means I'll check in with them each day to see whether I should come up the next, but it's impossible to predict anything. It would be easier to overrule their wishes if they were less capable, but they're both mentally sharp, and I think the same principle applies to parents that applies to kids: it's better to err on the side of respecting them when they say they're capable, even if that's scary.
Also, grief—there are no rules that cover everyone.