I glycol-ed my system but I had the ability to buy glycol wholesale direct from the supplier. I used 40% figuring I would want the ability to repressurize the system with plain water if I had to do a repair. With 40%, I didn't have to worry about some minor dilution.
The main reason I used glycol was I thought I might not heat the building at times.
I found it takes only a ton or so of coal to keep the building from freezing. I would not mess with glycol again.
Based on my experience, you would have at least 24 hours or longer in the coldest weather to get your system up and running again before worrying about freezing. It will take that long for the mass of the building and concrete to cool below freezing. Don't forget the soil under the building is also a lot warmer than that ouside and will take a long time to get to the freezing point.
Your biggest concern about freezing would be pipes that are not PEX and are smaller like for plumbing water lines. In many cases, Pex will expand a little and not split if you get a small frozen spot.