Permanent magnets start to demagnetise at something like 85c (185f) causing permanent damage. I'm not sure what temperatures the magnets zero uses in their motors can tolerate. I wouldn't trust their systems too much though. They have already proven they don't know what they are doing with their batteries e.g.. their charging recommendation to always keep it at 100%. They have finally corrected that per the large thread in this forum..
uhh not to be a dick dude, but practically everything you just posted was wrong.
while SOME permanent magnets have a curie temp that low, neodymium magnets come in diffrent grades, and have a curie temp range of 100C (grade M) to 200C (grade EH)... the magnets in your zero motor are not as hot as the thermocouple in the windings, AND that temp is still below the magnet rating... so its fine.
as far as telling people to not keep it plugged in 100% of the time, that depends. Do you care about the loss over time from battery degradation, or do you care that you can grab it at anytime and have full range? I only care about the latter. Like my cell phone, I keep it fully charged when I can, and if it drops too low for me to use I will just get another. That said, whats more dangerous to a lipo, being kept charged, or over-discharging, followed by recharging? If you know anything about lithium batteries, you would know that the chance of a short occuring after overdischarging is a big danger, while the staying charged isnt dangerous, it just shortens the capacity over time.
From zero's perspective, the danger is people letting the bike sit unplugged... NOT people losing a tiny bit of capacity over time. honestly if it was a major concern, instead of charging to max volts per cell, like 4.2v they would charge to something a bit lower, like 4.15v and call it 100%... oh. wait.
they are not stupid. they have guidelines because their customers dont know and are not going to learn electrical theory followed by lipo battery basics just to charge their bikes. think of the guidelines as the instructions you would give your mother or grandfather to operate it... not necessarily the cutting edge best advice, but enough that you dont have to worry about them... its simple, if in doubt, just keep it plugged in.
all this worry for loss that no one has documented happening on a zero yet.... mostly attributable to the fact they dont fully charge the battery. leaving off that last half volt per cell, extends the life considerably.
back on topic though... the monitoring system for the motor is simple, never let it go over a set amount, and then the magnet can never excced that amount. basic physics explains why that works.