I think it depends on what your goals are. If you want to move up in distance, sure you can continue to improve. But I don't think you can improve your 5k. I hate to be negative, but think about it. You'll have spent 5 years training your ass off and going to school on the side. When you start working 8 hours a day (unless it's really flexible) your training loses a little bit. Unless you've had a lot of injury problems holding you back, I just don't see improvement coming beyond 5 years of college running. Another aspect of working that has killed my running is sitting at a desk all day. Even with all the ergonomic gadgets, my legs are so tight when I try to run after work I just feel aweful trying to run. The hours in the day issue is a problem for me as well.
Here it comes, get ready to jump all over me...
This is exactly why I've moved to triathlon. It's a new challenge for me. I just can't improve running anymore, but I still have the need to compete. Triathlon is something I can accel at and see real improvement. Call me a sell out, but I'd rather take on something new and work to become better at it than to work my butt off to stay the same and gradually become a slower runner.