According to the help center:
What happens when a post is deleted?
Once a post has been deleted, it will disappear for all users except developers, moderators, and users with over 10,000 reputation. Deleted answers are also visible to the original author. However, deleted posts can be undeleted by casting undelete votes. Once a post has 3 undelete votes, it will no longer be deleted.
We can vote to reopen a question that's been single handedly closed by a mod, but not an answer? An answer with multiple up votes, that fundamentally answers both the posted question and op's actual problem.
Is this a bug? Or if it is by design, why, especially since questions can be reopened by community agreement?