This occurs all the time. AGRs are starting to become revolving doors as of late. You have to request curtailment, get a DOS/approved and make sure you're separated by the time you attend training, or attend it while on terminal leave. Otherwise you have to defer the training dates and let them make the decision as to whether they want to hold their conditional job offer or rescind it. Don't feel bad, there's co-workers of mine biting their nails doing the same waiting games over CJOs at Delta!
Legally, you could separate from the program, attend indoc, and drop long term mil leave on the spot (up to 5 years USERRA protection). But that would be really really really poor form. It's a regional I get it, but even that I think is a bit much.
I don't see the point over curtailing for a regional. A major I get. Unless you're sitting on a non-flying AGR. Good luck to ya.