This page provides a rules extensionEx that defines when a character can retire.1)
Since the early days of gaming, players have retired much-beloved characters after many levels, or otherwise having accomplished what they set out to do with that character. Sometimes a player may simply not enjoy playing a character very much. In a game with character stables, one might wonder how often a player can retire a character, and under what conditions.
Retiring a character frees up a slot in that player's character stable. There are a few ways to do that, detailed on this page.
Players have three options for retiring characters: character XP, character wealth, and session attendance.
Once a character has accumulated 20,000 XP, they can can be retired.
If a character owns 100,000 gp worth of items, creatures, and property, they can be retired. The sale value of magic items is used for the purpose of this calculation. Note that final wealth after any parting gifts (see “Requirements” above) must total 100,000 gp value.
Since it is only in extraordinary situations that a character will end up with 100,000 gp net worth before reaching 20,000 XP, it's unlikely that this option will be utilized.
For every 50 sessions a player has attended, they may retire a character with no XP or wealth requirement, even if that character has never been played. For example, if a player has played in 120 sessions, they would be eligible to retire up to 2 characters who fail to qualify for the XP or wealth retirement.
If an interesting opportunity presents itself, the DM may have the character return as an “NPC” in the future for some episode if the player is okay with it – preferably with that player controlling the character for the cameo.3)