If you delete the original comment, then you'll delete everything linked to it: comments, etc.
You could always amend the typo underneath to acknowledge your mistake:
"The sky is bluee."
Amendment: "blue*"
Also, you can comment and type "@", once you've done this begin typing a friend's name without a space and names will appear on a drop-down menu. Select them from there and they're then tagged and linked to the post via the comments.
These solutions aren't ideal, but at least you don't lose your comments. . .