Question

"Whatever is decided here." i think it's a sentence because it has a subject and a verb?

Answer 1

No, it's a fragment. That subject "Whatever" is the type of a pronoun that introduces a DEPENDENT clause. Sentences must be INDEPENDENT clauses.

http://www.chompchomp.com/terms/completesentence.htm

http://www.chompchomp.com/terms/fragment.htm