NeverarGreat said:

Speaking of highly convenient occurrences, Yoda's death seems to require more explanation than is given in Jedi. As it is, he dies five minutes after Luke arrives on Dagobah, a stunning coincidence. It could be that it was his destiny to train Luke, and seeing as his training was complete, there was nothing to prolong his life.

Actually, this happens in real life a lot. It is not at all uncommon to see a terminally ill person on the threshold of death to hang onto life for days or weeks and then die literally within minutes of some far away living loved one finally being able to make it to see them. We have a remarkable ability to fight and hang onto to life. If this happens in the real world you can easily assume a powerful Jedi master would easily be able to carry out the same feat, but perhaps in an even more remarkable way or for a longer time.

I've always assumed Yoda was hanging onto life waiting for Luke to return before letting go.