qs, yes, once you are checked to line as a second officer, it is safe to say your position is as secure as the next chap. (secure being a lose term these days)
Shortly,
what has the company to gain by summarily dismissing those whom it has invested great amounts of capital in training?
My guess is that it is a management level intimidatory tactic, just like kkken's threats over signing the AoA letter (which Nick doesn't think was a threat), just like the sickness management scheme, just like Cat B'ing guys for 'no particular reason', just like the sign or be fired letter, just like etc, etc