RE: Returning to training
short answer is no, you should get most of your gains back fairly quickly.
Long answer is it depends on how long you trained for to begin, how much you gained and how much you train now etc, but generally muscle size is in large part due to the amount of water that the muscles hold. When you train/grow you are doing 2 things, first is increasing the size of the existing muscle fibres, secondly and most importantly is that you are creating more muscle fibres as well. The gains you make when you return will be due to the muscles holding more water again, but because muscle fibres never disappear through lack of training, the ones you created the first time round will still be there and should grow quickly and you notice the gains faster.