I called Stations Casinos today about some total-wins futures bets I have sitting in the vault. They said that NBA, MLB, and NHL total wins bets are "no action" and will be refunded if you send the ticket to the address on the back.
I don't know about bets to win the World Series or the NBA championship, since those events will kinda sorta take place, maybe. But I would expect that those bets are "no action" as well, given the bizarre truncated seasons baseball and the NBA have had/will have. And obviously, NFL futures are still "action" for now, though I very much doubt the NFL season will go as scheduled.
They suggest you take a photocopy of your ticket, just in case. I would imagine all the casinos are running with reduced staffing and it might be a while before you get your refund.
(I'm going to get about $150 back on bets that were pretty much doomed if the season hadn't been cut off. Of course, there are other people whose bets were near-locks and will now end up with a push.)