The only times to retire a whole party/campaign is when the whole party wants to start something different and fresh or when the PCs actually "run out of meaningful" stories to tell because they already "did everything" and every further story with the old party would feel like that last cringey season of a show after you already had the most awesome finale possible.
There are games where the mechanics can break at some point along those journeys, but I have to encounter a system where the GM is unable to engage the PCs by providing problems you can't beat with a skill check/spell/power and still tell great stories as long as everyone is up for it.
I think you can't call out a rough area of XP to be done. There are way too many concepts needing very different amounts of XP to even reach their own goals. Some of them can find themselves struggling after reaching their first goal to keep them going after roughly 300 XP, while others are miles away from even seeing the finish line when reaching 1000 XP.
All of the games I played in so far were "considered done" due to other things than reaching any amount of XP and some of them went on for years. (Although I must admit we never managed to get to "max level" in DnD although that was because we didn't like the system itself too much
)