Just had same issue, see my post under Cedar Creek Slide Out Leak. Was caused by leaking black dacor material, which is becoming a very common issue. Had to cut out section and replace it. The video posted earlier shows the cause very well. I did install the slide skies that our dealer had in stock.
If the floor is wet and soft or dry and flaking apart it probably is not salvageable. I did find that on our unit the only thing holding the floor to the slide out were the small 1 1/2 screws that go through the drip molding, If for some reason these broke or came loose then you may be able to push the floor up and secure it from the bottom. When I replaced the new piece I did use 2 inch self drilling flat head screws and went up through the floor into the aluminum frame of the slide out. I sealed the screws with caulk. They were then also covered by the slide out skies, that were installed. I did this on both slides that have the dacor material below the drip edge trim. Hope this prevents it from occurring again.