Taking a week shouldn't really make nything shrink down that much. Just make sure you keep eating right and you be able to maintain.
It is. Training causes tissue inflamation and this goes away with some time off. I lose 0.5 cm ( + or - 1/5 inch) in my arms during the first five days off. Don't sweat it, you are not losing any muscle as long as you don't starve yourself.
Make sure during that week off you get massive protein.
you may loose some, bit over a year, your arms could be bigger overall.
When taking a week off do you guys eat as much as when training? To me it would seem like you burning less calories. I know you grow outside the gym, but for how long? Same thing when taking only 3-4 days off on the last day should you lower food intake?