His long-dead wife turns out to be alive, so he no longer wants to be an adventurer.

The entire party are captured and enslaved. The PCs are together, so they can escape together, but he was taken elsewhere.

As the party approaches what is expected to be a huge treasure, he slips away. The chest, when opened, contains a note from him. "Sorry, mates. I couldn't resist. Pirate, y'know"

The duke's daughter you rescue falls in love with him, and he retires to a life of ease.

They find a pirate ship who needs exactly one more crew member, and make him an offer. (And you can re-introduce the ship, with him as captain, sometime later.)

As the temple of the pirate goddess collapses, the goddess herself appears and claims him as her next priest.

The party finds a magical one-person boat. One day it, and the pirate, are gone.