the old 'oh, well they could just leave' was bound to turn up. no, you can't 'just leave'. you can apply for premature release from your contract if you have not already been warned for ops. the military are under no obligation to release you if they judge you are required and it is within the terms of your contract (ie the period of time you have signed on for).
when i joined the military, i was required to sign a form to say if i dared to get married or pregnant i would be required to leave. end of. i see that would sit quite well with some of the posters on here fortunately the european court of human rights thought differently. presumably this couple met as serving soldiers, fell in love, got married, and had a baby. y'know, just like any other couple on the planet.
if you could just leave, or decide you didn't really really fancy getting shot at this month, ta very much, it wouldn't be much of a fighting force. individual soldiers/ airman/ sailors don't make the decisions. this couple may have agreed a deal with the drafters which they thought was in the best interests of their family, or they may have been making the best of a bad job.
without knowing their family (or their extended family) how on earth can anyone judge whether this was the right or wrong decision? only time will tell.