The party's level 17, so Epic Level--read: "your path to Godhood"--is right around the corner. Interestingly, it seems like this would be the best possible time to do flashbacks--coming to terms with your immortality, in a manner of speaking.
I'm imagining a "Golden Years" movie where the main character goes back to the place where he proposed to his fiancee, or the "wild travel adventure Senior Year buddy flick" stereotype. There's a LOT of weight on the character's shoulders--soon he's going to become so world-weary that he retreats to his study, or takes on the mantle of king/dark lord, or renounces his humanity and become a (check one: god, elemental paragon, world spirit, lich).
This is a perfect time to ask, "what happened to his first girlfriend/boyfriend?" "Where's your mentor now?" "Were there kids?" "Are you the home town hero, or have your enemies razed the village of Hammthorpe to the ground as a message to you?" "What parts of your life will you take with you into the divine realm?" Remind the hero what he's giving up--or what he's fighting for--before his journey into the underworld.
The flipside of this: All characters are orphans, and very few of them have a past that ties them down. That's why they're able to be adventurers.
A bit hard to do with a large party, particularly at a time when the campaign is going to start literally getting epic, but still, it just seems like a golden time for looking backward.
Anyway, ramble ramble.