Currently, spam flags and rude/abusive flags age away in 2 days if not acted upon. This doesn't really happen on active sites, but it does happen elsewhere. (For example, I have four aged-away spam flags on Chinese Language and three on 3D Printing. And had a bunch on Русский язык before leaving that site.)
I don't think this aging does any good at all.
- If a flag is invalid, it should be declined.
- If a flag is valid but moderators are offline over a weekend (which is understandable), the flag should wait until they come back.
- If a site doesn't have any active moderators, aging away flags is solving the wrong problem.