Is there a regime in which you just cannot get out of it?
some t-tail jets, the BAC-1-11 had a famous one during flight testing, have deep stall tendencies, where the horizontal stab is rendered useless...in an airplane with a conventional horizontal stab, it seems impossible, provided sufficient altitude is available to recover...even the 727 was found to NOT be prone to deep-stall tendencies...in the AF crash, it appears no positive effort was made to recover from the stall...simply lowering the nose down 5deg is not sufficient to reduce angle of attack to below stall when the aircraft flight path is much greater..Airborne Express DC-8 on a test flight is another example of flawed stall recognition and recovery training...