Conversation so far:
What was Michael Anthony (musician)'s role in Van Halen?
Anthony played bass on only three songs.
what caused his role to start diminishing?
As early as 1996, rumors periodically surfaced that Anthony had been fired from Van Halen, despite claims to the contrary.
Was he actually fired?
CANNOTANSWER.
WHen did he leave the band?
2000 and 2001.
Anthony's name was also credited in a few band newsletters and appeared in band interviews during this time.
Sometime after this, Anthony disappeared.

Question: where did he go?
Self-contained rewrite: Where did Michael Anthony go after leaving Van Halen?