BookBarbarian
Expert Long Rester
The medusa description in the MM is very specific about how to end the petrification: The petrification lasts until the creature is freed by the greater restoration spell or other magic.
In my current campaign, one of the PCs was turned to stone by a Medusa and after the rest of the group killed the Medusa they took some of her blood and found an alchemist to make a potion to restore the stoned PC. Something like that could work.
Let them make medusa blood stone-to-flesh potions.
Edit: Technically "oils".
I'd let potions brewed from medusa remains fall in the "other magic" category specified in the monster text, but not go for the killing it ends the effect option.