If I drop off one of the ファン will he/she get e-mail that I am no longer a ファン of him/her?

Nope, but their ファン number will go down.

No, あなた only get messages when someone ファン you.

Their number will go down, but depending on how many ファン the person has and how often they're added によって people, they probably won't notice if あなた drop them.

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the number will just go down like once someone faned me and didn't mean to so she unfaned me and it just went down : )