I think many long term disability insurers will not be prepared to consider a buy-out request, and if they are, they may not be prepared to pay an amount that would be acceptable. Insurers would be suspicious regarding the motivation for such a request when monthly benefits are being paid, and will usually only consider paying out the claim for a significantly discounted amount.
Perhaps there are other options that you could look into to get money…or if debt…maybe speak to a trustee.
I think asking for a buy-out is asking for trouble. Some circumstances may warrant such a request…but be careful…