If we update a variant in the Epi catalog by an external system will the update to the variant cause the variant to be removed from any content blocks its been added too?
I don't think it will be removed if you are only updating it because in database content link will remain same. Its same concept like if we move one page from one location to another it keeps it's connected link intact.
By what mean is it "updated"? If it is normally updated (i.e. one or more fields are changed), no. If it is deleted, still no :)
Brilliant guys that answers my question :)