For context, let's say you roleplay a character and have done ever quest relevant to their story/personality. What do you do to stay entertained?

i would retire them if they dont have more story to go and I would start a new one OR you can just lead him to another way of his story maybe something he wasn′t expecting, if you don′t mind what story does this character has ?

Glitches and Exploits to the max!

Start stuffing Horses in your house with Wabbajack

Most of my characters have a limited role, as in they will do certain factions and not others. When they are done with what I have created them for, I either retire them to a nice place to fish, or I go collecting. Collecting things puts a different perspective on the game and I can spend dozens of hours chasing down whatever it is I am collecting.