[Pull Toy]

I personally would gravity drain and blow out all lines. (Don't forget the washing machine spigots, if so equipped.) You also might want to put some anti-bacterial into your sink traps, to eliminate any storage odors

My thinking is thus:

1. Depending on your water quality and possible bacterial count, why risk the possibilities of long term contamination, algae, or anode degradation in your HW tank while not in use.

2. You will have the excuse you need to remind you to re-sanitize your whole system, when re-energizing and going back into service.

Good luck with the surgery!