Bypass boiler tankless hot water coil while still running the boiler to heat the home?

For several years we have been completely shutting down our home in Alaska while we snowbird in Arizona. For the first couple of seasons we used compressed air to purge all the domestic water lines, toilets and appliances. Then drained the boiler and used compressed air to blow all water out of the zones.  This has worked out fine.  We did switch to pumping RV antifreeze thru the domestic water system a few years ago because it was easier and faster than using compressed air.

This year we want to keep the house heated but as an extra precaution continue to protect the domestic water system in case the boiler fails.

Option 1

Install plumbing to bypass the tankless water heater and use RV antifreeze for the domestic water system. 

Will leaving water in the closed tankless heater be a problem?

How would you plumb the bypass? (See pics)

Option 2

Use compressed air to purge all the water out of the domestic water system.

Will leaving no water in the tankless heater be a problem?

Thanks in advance

Well McLain P-WTGO-5