I have no problem with Yoda expiring when he did. It's a dramatic device as old as most of the mythology Lucas draws from. He looked more frail than when we last saw him in ESB, and was probably using the last of his force abilities to hang on as long as he did. Dagobah isn't exactly the best climate for a 900+ year old guy to be living on alone for twenty years.

One of the puppet's eyes actually went askew on the set, but they decided not to fix it, as it helped with making Yoda look ill.

I'm still amazed Frank Oz and company pulled off the shot of Yoda climbing into bed. Who needs CGI? ;)