I hadn't thought about that. UA's reluctance might depend upon the reason for the original cancellation.

That said, I see exactly one viable route tonight with 4 seats in P+ -- there's an Austrian flight out of JFK at 9:35 PM, and a five-hour layover at Vienna, with five seats available.

Tomorrow, UA claims that there are 4 seats available on SN from JFK-BRU, but the native flight number only has 1, so I don't know if that's real inventory or not. That's the only option that comes up.

(In other words, travel TATL, for four people, is extremely limited in PE right now).