When you squash merge on github the new commit references the old PR. If you don't delete branches on merge you would keep the commit history on that branch, but then you have to battle with branchs persisting forever.
You’re translating the problem from : searching through branches that are named according to their ticket and what they are meant to accomplish to: complex and not-context-free git bisect.
“try-again-something5” doesn’t cut it but “$ticket-at-least-five-words-here” does.