Without me and others like me, You never wrote those songs.
Same can be said for any other instrument..
Depends on who's doing the majority of the music writing and/or lyrics.
It isn't any easier to replace any other instrument (If the person playing whatever instrument is very talented) over drums.
Just depends on who's at someones disposal.
These days there are musicians that can play as good as anyone else.
There are musicians by the boat loads, that can play as good as any musician before them..
Some bands chose not to continue when they lose a member, mostly out of respect and/or legal matters.
If I were a manager and I had to pick a Van Halen member to get rid of but continue on with the band to make money.
I wouldn't even hesitate to get rid of Alex Van Halen over Eddie.
Depends on the circumstances..