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!
Steve & Jan, Ava & Emma (Mini Schnauzers):
2016 F350 Lariat 4X4 Powerstroke CC/SB "PULLTOY V"
2013 Alpine 3535RE "MAGIC CARPET IV"
Proud Navy Vet!