What happens if my orders aren’t corrected in time for my re-class?

If you're actually a SSG you aren't authorized to attend that MOS, so you are saving yourself sometime of being turned around from the school house.

You can go to your career counselor now and process a renegotiation of your contract. You will be offered what is available for class seats that you are eligible for. If you cannot come to an agreement with HRC, you may request to cancel your contract

You are not eligible to receive another 68c class seat because of your rank. If you show up without a grade waiver the school is required to send you home. 68c does not do grade waivers for SSG, the MOS only accepts non promotable E4 without a grade waiver. 25e would be a good choice for a staff sergeant to choose as an alternative

I should also point out that this is not a simple amendment of your orders. Your Phase 2 is a PCS location. Your entire PCS location has changed. That means you would have to redo the levy brief and levy packet, complete the orders process and get a whole new set of orders. Even if HRC placed you on a new assignment today it would take a week tk go through the validation process before your reassignment section could process your new assignment instructions. Fort Campbell can't release you because you have orders to the wrong PCS location.