I have read you are not suppose to let anti freeze in the hot water tank. The valve lever breaking off has nothing to do with a frozen line. It was 60 degrees when mine snapped off. I have taken the broken valve apart and concluded its a cheap poorly designed excuse for a valve. As for the low point drains, good luck with that since on mine they are not the lowest point on the system so water will still be in the lines somewhere along them.
Best thing to do is replace these cheap valves before they gice you trouble. Most expense is the actual tool to crook the PEX clamp with. The band PEX clamps are cheap a bag is a couple of bucks.
2012 Fun finder Xtra XT-276, Pitbull strapless restraints
2016 GMC Sierra Denali HD Duramax/Allison 4wd
WERA Expert #826