For one, there is no way he drops right now. He'll further stall and request a full-court hearing. Whether he gets it will be determined.
What will he reveal? Everything he learned when he was head of Defense Intelligence:
Activities of CIA
Involvement of CIA, Obama, Brennan, et al in creating and sustaining ISIS
Specifics of Iran Deal (money flow, who benefited, etc…)
Any activities of subversion of U.S. interests (treason) involving high government officials (would've been learned by military intelligence)
I'm sure there's much more…