the #hash part for deep-linking to anchors

Oh... So you're not talking about path parts. You're talking about fragment parts — URI parts

So in some sense this is a form of link rot. I think there will always be some risk of this, since we don't have any control over how any external web site manages their anchors — nor indeed their paths — nor indeed even the domain names.

It's the nature of the beast. People put external links in their posts; ten years later those links don't work. We just have to live with the risk.

In general, I'd prefer to stay with perldoc.perl.org, since it is "official". I think we'd need a really compelling reason to switch to something else. Like we did with MetaCPAN.