I’ve weigh-lifted off-and-on for the past ten years, and something I’ve always noticed is that it takes intensive effort to increase strength and fitness, but much less to sustain it. This Times article corroborates: http://well.blogs.nytimes.com/2010/12/29/phys-ed-if-you-are-fit-you-can-take-it-easy/
One thing I’d add: even if you lose weight-lifting gains over an extended period of time, (by, say, quitting altogether for six months or so) you will be able to regain them very quickly, especially as opposed to a novice. When I first started working out, it took me about six months to go from a 155 bench to 200. I quit for a year (I’ve never been able to motivate myself to consistenly exercise for longer than a few weeks at a time), but when I started again it only took me about a month to go from 165 back to 200.
The upshot: even if you are positive your schedule or personality won’t allow you to keep up a consistent workout schedule, when you find yourself with time on your hands go ahead and hit it hard for a few weeks. You will be able to sustain your gains with fewer workouts after the spurt is over.