Yes. I had been on Rogaine since 1990 (2%, then 5% in 1998), a long time... from then until 2003, the sh*t was working, but I didn't know how much it was, or how well it was working.... I do now.
In June of 2003, I decided to drop it....no real reason...just been so long on it with no cessation.
Flash forward to Oct of 2003, I was then dealing with about a 40-50% decrease in hair, a massive difference, so much so I couldn't wear the same style I had from the prior 13 years. It was horrible.
I immediately got back on Rogaine and within 3 weeks it had all come back (early-mid Nov)... I'm not lying, it was the damdest thing, as I thought it would take at least 3 months (the normal growth phase).
Been on it since. To answer your question, you'll grow back the lost hair, as long as the cessation of Rogaine isn't for long, long periods of time (years).