I'm sure there would be people in Yahoo would want to help, the problem is actually finding and getting in contact with someone who does care.
...then clearing it with legal and getting approval within the org to actually /do/ this. AFAIK, this would be unprecedented, but would probably win Yahoo! a lot of fans when they need it most. I have no real hope for them or anyone in a similar position to provide user data back to community custodians.
.. as long as you forget all the other user-generated-content sites Yahoo has closed over the years.