I go a completely different way on this.
The whole point of the Prequel Trilogy (to me) is that the Jedi were doing things the wrong way and wound up getting destroyed because of it. The only Jedi who got it right was Qui-Gon Jinn--rather than listen to the Jedi Code and the millenia of assumptions made there, he listens to the Living Force.
When the Jedi die in the Geonosis Arena, they are gone. When Qui-Gon died, he continued to exist as a part of the Living Force, to the point where he could communicate with Yoda (seen in AOTC) and eventually Obi-Wan (cut from ROTS).
Yoda sees the triumph of Qui-Gon at last when he is nearly defeated by Sidious. If he had died then, it would have been over. To truly be able to defeat the Emperor, he will need to be able to go on even after dying. So he goes into exile, to learn from Qui-Gon's spirit how to fully commune with the Living Force, and effectively admits the Jedi Order was wrong all this time.
None of this even touches on the Skywalker kids (who I think Yoda did not want trained, but that is a different subject entirely.)