This kind of scenario is the most likely catalyst for me doing so, closely followed by recycling concepts used in 1-shots (like tournaments or the like)....if I wrote a ton of backstory, had lots of stuff planned, only for Timmy to get critted by a goblin at level 2. I'm sure as hell reusing them. Not in the same game, or even with the same group. And possibly reworked heavily to fit in the setting. But I'll be reusing the core principles as it would essentially be a character I was excited to play, and didn't get to.
I was literally just about to come in here and say basically exactly that!I reuse them sometimes as NPCs when I DM, as it can be both fun to revisit an old character and saves a lot of trouble in developing more interesting NPCs.
The downside is that, since they are themselves a capable adventurer, you need to have a strong reason why they can't or won't join the group or the group may try and recruit them and get you locked into a DMPC situation.
I do that now and then (not just my own PCs). I just say that they have other priorities or commitments. Can be anything from "research" to political or business responsibilities.I reuse them sometimes as NPCs when I DM, as it can be both fun to revisit an old character and saves a lot of trouble in developing more interesting NPCs.
The downside is that, since they are themselves a capable adventurer, you need to have a strong reason why they can't or won't join the group or the group may try and recruit them and get you locked into a DMPC situation.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.