I would treat it as a make-up game or like pre- or post-bowling where both teams are present (i.e., not unopposed). The teams should decide when they can both get together to bowl the tiebreaking game and a league official should be present when they bowl.
If nothing else, have it done at the awards night. If you normally bowl at 7, then all parties involved should be available then anyway, so get those teams together at 7:00, bowl, then hand out awards when they're done. Or even while they're bowling.
As a last resort, if they cannot agree to a time, then bowl separately. There was another thread here about a team pre-bowling, deciding the lanes weren't to their liking, and declaring those pre-bowled scores as not legit. They wanted to bowl league night and just take the blind scores for the absent members. If the one team has already forced the issue by bowling (and it was witnessed by a league officer), then those scores stand. No pooh-poohing allowed if they lose.
SH