The modules@perl.org team (mainly Brian Foy, Andreas and myself) have been handling this for years.

Module takeover is handled on a case by case basis, with the general standard being "A number of contact methods tried a number of times over a number of weeks".

You'll then be given co-maintainership.

If the original author returns, they retain control.

Often, they'll just hand you primary if you show an interest.

But this is a solved problem.