In that hypoethical scenario, I'd say yes, the abductor would have assumed GM to be back at the table by that point. The conversation with JW was pure chance, had he not bumped into him he would have been back with the rest of the group when Tannerman crossed the road. Hard to say whether he knew GM's face or the Tapas routines. If the abductor was forced to hide when GM entered, it might suggest perhaps not. But then again, his plan may have been to lie in wait in the apartment and as soon as the first check was done, make his move. Giving him the maximum amount of time possible to get away from scene before the discovery is made at the next check. It would make sense that if the abduction was planned and that the apartment/Tapas group were being watched, the most logical time to strike would be immediately following a check.