I'm so going to smack everyone in here...
Jedi don't carry 'spare lightsabers' unless the situation calls for it (like arming another Knight, i.e. Anakin and Obi-Wan in the Arena). Otherwise, they only have one (or two if they use two at once). Yoda had one and one only.
Yoda dropped it and did not retrieve it.
it doesnt matter what happened to his lightsaber.
i understand the question of what happened to dooku's, since
it just mysteriously vanished from anakin's hand. that i can deal with.
but these "what happened to this thing that doesnt matter" threads are lame.
hey, whatever happened to the heads of those clonetroopers yoda decapitated? did anyone take them? did they just leave them there to rot? did they get a proper burial? does anyone give a shit?