Even if it does, remember that so much of Disney is inside. So as long as you are prepared to walk from attraction to attraction in the rain, your trip will be fine!
This article made me feel much better about the prospect of rain.
I used it to gauge what attractions I may want to move to first thing in the morning if the rain forecast was still looking bad for the day and closures seemed likely.
It is a little outdated, so add 7DMT to that MK list