Again, the rules are made up, but there are a dozen listed sins that are unforgivable. You just have to look for them.
However, a deal with the devil is automatically considered blasphemy against God, and thus an unforgivable sin. Add in the sin of Pride, and Johnny is damned.
Pride might be forgivable, but the prideful rarely ask.
And again, a deal with the devil is by definition, a rejection of God.
Also murder is on the list of unforgivable sins.
Because there are five or six places in the new testament alone that list unforgivable sins.