I've had a couple breaks in training. Started in Tang Soo Do as teenager, stopped to go to college. Dabbled in a few arts (Aikido, Hwa Rang Do) before settling in on MJLH Kung Fu (a Northern Shaolin Style) in medical school. Stopped for Internship/Residency/Marriage/Children, restarted 10 years later in Seven Star Praying Mantis, been with it for about 3 years now.
While my brain had managed to forget all of the sequences of my previous style's forms, my instructors have said they could see that my body had not forgotten how to move in the appropriate ways to execute techniques (in forms and application, open hand and weapons). Of course, not everything was the same across the styles, so I had some unlearning to do as well.
Perhaps the most important thing I learned in taking MA up again after the break has been a truer appreciation for martial arts and a greater capacity to invest the time and effort required. Most days, I try to get to my school 30-60 minutes before class to review previous material, etc. I have told many people that one of my great regrets is that I stopped practicing my forms and drills once life took me away from my teacher.