I think that Act V should still be part of the play. Not only does it fit Shakespeare's five act play format, but it also wraps up the play. Without it, we have Portia and her maid leaving with the rings, and the others have no idea about their involvement. But when you add the last act, all of this is sorted out. Portia has a bit of fun teasing her husband about him giving the ring up, and then reveals that it was her who saved Antonio's life as the judge. (He also finds out that he still has a few ships left too). Then everyone is happy and getting married, and the play ends on this upbeat. I think that is its main role. The final act ends so happily that the audience forgets the tragic ending of Shylock, and I think that's how Shakespeare wanted it.