I started collecting thousands of URLs (as resources for notes) about 16 years ago. In use, I'd estimate that link-rot has affected about 1 or 2 out of four in that time. Out of those two fails, I expect I'd recover about half by feeding the URL to Wayback and asking for their oldest save. That tends to be independent of age.
Most successes are from reliable sources.[1] When those sources fail, it's usually because the resource is still there (in identical or revised form) but has a modified URL. They're often recoverable by searching by 'site:www.abcd.efg ' and a string of terms from the original.
Each fail requires that I consider whether the time to recover is worth it. I also imagine how difficult it'd be to have saved each resource, and have to search for it. Ideally each resource would have an ID and permanent online home; unlikely.
[1] Each fail continues to teach me which specific resources are most reliable over the long term. Short answer:References and WayBack.