I think it should continue past, he should meet the mother, screw things up, and hijinks ensue. They could easily spend a season or two on that, and truth be told, that's the most tenuous reason we watch the show anyway, it's the interaction between the main cast. They just have to find the right person that can be added, and the show really can go on for a while, who knows how long they dated and it took them to get married. That seems like the natural stopping point, and the writers could really take as long as they pleased on that, as long as they keep the funny. I'm happy to follow these friends as long as the show makes it fun.