Feature summary:

There should be a special page at [[Special:Brokensectionredirects]] that should list section redirects whose target heading doesn't exist.

Benefits:

Would allow the detection (and fixing) of broken section redirects.

Notes:

See also T395298: Throw error message on attempt to create "Broken section redirect" to section that doesn't exist on page that does exist. -- these might be able to use the same function.