Who knows, maybe in the future modifications will be made that allow certain higher ranked members to remove certain types of flags.
I think the option for someone to erase their own flag should definitely be considered, but I'll save expanding on that point for a different thread...
Maybe right now that is something just not on the agenda because of the recent introduction of 'bump' but if someone opens a flag it stands to reason he should be allowed to delete it especially if the point of dispute is resolved.
Having flags active for a minimum of 3 years is quite excessive if two parties involved find a solution and no longer have a dispute and harsh if both parties want the flag removed.