I'm not sure if there is an official known despawn timer for player bones on retail (and especially I couldn't find anything for how it was during vanilla).
I would say 24 hours is a decent number. However, I am almost certain there's more to it than that.
I suspect there is either a maximum number of corpse bones that could be create either per player (maybe 5) per map (maybe 5000) or per server (maybe 10000).
Some tuning of course to see if it looks right.
A periodic (once per hour maybe) cleanup could be performed to clear out anything above these limits (oldest first of course).
Just how I think it should work to look like the real servers. For sure, during world pvp there are a lot of corpse bone piles visible. But I've never seen the kind of numbers seen here. No matter how big the world pvp event. So clearly there was some limiting factor going on, and I don't think it was just population size.
As for there being no performance impact. That's surely not true. We can call it negligible, but it must have to send information about every bone pile to every client that enters the visible area. That's not zero processing. Bandwidth, again it'd be negligible I suspect.
For sure though, this is a really low priority thing in the grand scheme.