As has been said above,(most)comedy songs are akin to telling a joke - generally, once the punchline has been delivered it becomes a spent bullet.
There are exceptions of course. Fawlty Towers (though not a song)is a good example of comedy writing that is eternally funny because of its consistant high quality. In the same way, comedy songs written to a similar level will always survive (providing the content does not get dated). It's worth remembering, there's a whole new generation every couple of decades to whom the song(s) will sound brand new.