We are in the same boat, although typically, I would have no problem getting the spend in over the 24 months (not sure now). If you wait, you are hoping basically hoping that United significantly reschedules your trip (at this point more than 6 hours change) you can get a full refund. It's extremely likely many international flights will be canceled or moved enough to qualify. But SOME of them will still fly, and its a gamble if it will be yours or not.
If you take the gamble and lose, you can still cancel your flight and reuse the ticket, but you'll lose the change fee. I don't know what type of credit (12 month, 24 month) you'll be able to get at that time, but it seems like it would be a 12 month future flight credit minus the change fees.
The other thing to know, if if you cancel by April 30, you'll get an ETC, which you can use to book a flight for anyone (not using partners) so even if you won't use the credit, if you have friends or family that might, you might be able to work out a deal.
I'll likely be cancelling by April 30th.