My first post in ages, and of course, it's because I can relate
I dislocated a rib back in October, and just as I was about fully recovered 2 weeks later, I became so busy with holiday prep at work that I decided to take my longest lifting break ever - 10 full weeks of zero training. Even when I was practically crippled from my back injury in years past, I still did some training with never more than a week off. Here's what happened this time around -
Physique-wise, I decided to let myself eat junk food and far too many convenience meals (not a good idea) and I ended up putting on 10 lbs. over that short of a period. Mass-wise, I still looked the same, but there was some definitely regaining of fat on my midsection and lower back, and almost 3 months back into training, I'm just about where I was pre-break. That part wasn't too bad, easy enough to fix. As I've found from personal experience as well as from those I know who have taken significant breaks, the longer your body has been holding added muscle mass the easier it seems to be to retain even if you don't train for a good stretch. But, that leads to....
Strength-wise, it has been the hardest. My max strength on everything dropped by about 10-20%, but not only that, my conditioning went to hell and so did my ability to rep out the same weights that I could do high volume sets with. Where I did a pretty easy 3 sets of 10 @ 405 lbs. for deadlifting back in the fall pre-injury, I almost died trying to do 405 for 1 rep on my return. Everything that was easy was much harder coming back, so while I was able to undo the physique damage in about the same time as I took off from training, the strength part is going to be a longer road back and might take me until summer to get there.
So, in retrospect, shorter breaks tend to do the body good as 1-2 weeks off won't kill you and won't destroy progress unless you're on a tight program schedule for competing in something, but once you go beyond that 1-month mark, be ready for the fact that it's going to take you a while to regain what you lost along the way.