In Linux terminals, you probably could have pressed Alt+F2 or Ctrl+Alt+F2 (F2 could be other F-keys) and log in on a second terminal to recover (by reading the manual or killing it). Also, if bash already had job control back then Ctrl+Z would have suspended vi/vim to the background.
I’m writing this, so people try it and maybe remember it, if they get stuck in some program. Doesn’t have to be vi. Maybe you just launched a long dd command and don’t want to end it, but want to look something up. These hints may help then.