Sesame Street revolutionized TV and the way the medium is used to educate children. While I also yearn for the days of old, the show is obviously still popular and relevant. Sure the puppeteers and human actors are getting older, but so are we...the audience. As I am sure most of us here are, I am a devoted SS fan and always will be, but remember something here, the show is targeted at children. While we remember Jim's Ernie, Frank's Bert, Mr. Hooper and Roosevelt Franklin, today's preschoolers don't even have an idea about any of that or any of those characters.
A classic TV network (TV Land, for example) running the old episodes or more Old School DVD's for us veteran SS fans is great and at the same time, we get what we want and today's children still get out of the show what they want and more importantly, what they need.
So I guess my answer is no...do not cancel Sesame Street ever. It is still my favorite show in the history of Television and I'd like to see it out live me.