From my understanding, the Yeti sort of threw out its back one day... would fixing its back really only take a matter of months?
I would have thought they'd have to close down the whole ride to properly fix it.
My husband did a thing with the imagineers a while back that discussed the design of EE. It is actually 3 completely separate structures built around each other- the mountain, the track, and the yeti. So, from what he was told about how it is made, it is possible to disassemble one part without bothering the other 2. It might not be easy, which would explain the delays, but...