I’d just ask the players what their plan would have been if they’d known the missing player would have been able to play in the next session. Then, I’d let them work that out as if they’d taken that approach from the jump.
Or, if too much happened after petrification, I’d have someone in town know how to make a potion of unpetrification, and the rare ingredient is something they have, and the NPC is down to barter for the service, bc her landlord is a total slumlord who is trying to extort her over supposedly unpaid rent, or somesuch. Visit landlord to talk “sense” into him, and you find him in the midst of something dangerous and illegal, and he attacks.
I’d have the potion work before the fight, so the absent guy can play. If the group is the type that might take the potion and bounce, have it require multiple treatments for the effect to stick.