Well as someone said earlier, it really depends on each individual character but here are some of the things that my characters did after stopping "adventuring"
A fighter of mine in FR got married, settled down had kids and opened up a brewery. In time wife died because of the flu, and kids grew up and went their ways, except for the oldest girl running his tavern and his younger tomboy daughter. He is very bored and misses his old life most of the time. He is coming out of retirement (he's 60 now) for one last time, as his wizards friend(another retired PC) calls him up for one last quest. We'll play this game in the summer.
A wizard of mine was very talented but succumbed to the lure of the dark side and committed terrible atrocities to gain more and more power. In the end, he was stopped by his son, and reclaimed to the good side (kinda Vaderish). He spends his days in his tower far to the North these days, doing mostly research and other stuff. He is repentant, but he still bears the burden of causing all that trouble and all those deaths. In time, he will be played once more as a mentor and an advisor when his grandson(or some other younger relative) chooses the path of the mage.
Got a rogue that hit the jackpot. But he blew away all his money on drinks, gambling and women. So he might make a comeback too..
Well I guess characters never really retire when I am playing them... Kinda like a long mexican soap opera...