I'm just curious to here the forum's opinion on this topic.

If it's a PC, then there are several answers:

• When the character is killed. Being dead significantly limits a character and may reduce the player's enjoyment. Beyond that, most players have difficulty roleplaying a corpse.
• When the player is no longer interested in playing the character. Depending on a variety of factors, the character may continue to be used as an NPC.
• When the player is no longer interested in playing with the group. Depending on a variety of factors, the character may continue to be used as an NPC.
• When the character no longer fits with the group. If there is a big enough issue that the players cannot resolve, an 'outlier' character may need to be trimmed and replaced. Depending on a variety of factors, the character may continue to be used as an NPC.
• When the GM ends the game. Depending on the GM of the next game, continuing a character from a previous game may be possible.

Simple answer... when its no longer fun to play them.

Factors as Happy has noted above will play into this.

Are you no longer having fun playing that character?

If the answer's "Yes," then it's time to consider retiring the character from an ongoing campaign.

As long as you're enjoying playing that character and the campaign isn't coming to a close, then you can keep on playing that character no matter how much XP you've accumulated.

Granted, once the PCs start nearing the 2000 earned XP mark, the GM's probably going to have their work cut out for them in terms of challenging a group of such mighty individuals, but I'd wager most campaigns will have come to a conclusion long before that point.

When your GM is committed.

If are you feeling that something fails, first explain it to your GM or players.Try to fix and change it if do you still believe that something is still alive with that char/game, BUT, if after the talk you don't see any sollution, just make a last and final epic session to say good bye (maybe this will turn again the flame ) and just continue with another character or game.

There is a "not so common" option that is export the character to another group or game that the entire party and the GM think that will fit properly.

Of course, anwers given are pretty good