I don't believe Nemesis was really intended to be the last TNG film. I think everyone involved knew there was a possibility this was going to be the last film which is why the decision was made to give the film some sense of closure e.g. Riker and Troi leaving the Enterprise, Data dying and Beverly going off to Starfleet Medical ( those scenes were cut from the movie though). I remember when the movie was coming out, some of the cast expressed their surprise at Paramount Marketing's slogan 'A Generation's Final Journey Begins.'
Long story short, if Nemesis had done good box office, they would have made another TNG movie, there's no question in my mind.