Thanks for all the responses here, you guys got a lot of good advice...
But,I 'm not so much worried about allowing players getting their old characters back by what many of you suggested or even other means. There are a lot of other ways to bring these old characters back to flesh, which i am not opposed to.
I'm just concerned about the death of medusa being one of those possibilities. I'm not even entirely sure why i feel this way actually. I just don't see it as a feasible way, and think some of the suggestions i've heard on these boards as more feasible. But the players insist that the medusa's death be the main reason the old characters become un-petrified. ...They dont want any other reason!!
To add more depth, we are playing Tomb of Annihilation, and the players original characters got petrified in Nangalore by the medusa there. This is a very remote part of the jungle that doesn't get a lot of traffic by the world at large. The players new characters valiantly defeated the medusa, and now want thier old characters to suddenly become un-petrified.
I have previously allowed the old petrified PCs to become un-petrified by the Red Wizards, an evil group of mages who are competitively focused on the same quest and might discern the statues as potential helpers, ...AND... ive even given the players new characters access to an item with the Greater Restoration spell (3 charges max), so they can pick and choose who they want to bring back... Im even willing to spin some of the other suggestions offered by you guys here in this post.
but for some reason, they dont like or want those other ideas...they want the death of the medusa to un-petrify everyone. To me, i just dont think its plausible for the death of the medusa to revert the old characters back to flesh. And believe me, i see no problem with them having their old characters back...i just want it to make sense...and for some reason, im struggling with the death of the medusa as making sense for that.
My players just want me to "go with it" and DM override any rule, which i am reluctant (but willing) to do...i just think its a sucky answer, and hoping that someone/anyone can spin me a better reason besides DM override why the death of a medusa would suddenly bring back "everyone she's ever petrified" in her life (including the characters)