Aha - I saw Mr. Seidelman's name but did not recognize the picture of him on IMDB so didn't make the connection...
Jerry did leave the show for a long time and came back this season as other characters were making guest appearances. I guess he works for less money than George Clooney as he in most of the episodes instead of a guest shot or two.
I was a little disappointed in the finale - I thought it a bit bland on the story lines though I guess their intent was to stay true to the original spirit of the pilot. Several episodes this season got back to the great writing that made this show so interesting to watch. I will miss it. But like other shows that eventually ended - Bob Newhart, Cheers, Friends, Hill Street Blues and the Paper Chase - life will go on after TV.