I don*t want to loose my gains while pursuing a career

As for most of us, the thought of loosing gains is probably correlated with some degree anxiety? In times of high work load outside the gym, how little can I train/week and still maintain? So that I can optimize whats's, at that time, most important?  

Some studies claims that you need half the volume to maintain, in relation to gain, your current muscle mass. Thoughts?