By way of quick comparison and getting things into proper units
82,000 lbs = approx 37,000 kg which is fully laden total vehicle weight (cab + trailer + load)
Raising (say) 30 kg of neo magnets from (say) 0 deg C to (say) Curie temperature of (say) 300 C is 30 x 300 = 9,000 kg.C
In comparison with (say) a 1,000 kWh semi battery (inc unavailable portion) at (say) 6 kg/kWh = 6,000 kg battery (13,000 lbs approx of 27,000 lbs cab kerb weight)
Raising (say) 6,000 kg of battery from (say) O C to (say) ideal battery charge temp of (say) 30 C is 6000 x 30 = 180,000 kg.C
So indeed simply dumping excess heat into the battery gives 20x of heat reservoir compared with 'just' letting it accumulate in the neos. Of course it wouldn't just accumulate in the neos as the motors etc are of the order of a few hundred kg in toto, and indeed there is already a wet-loop cooling system in there to do just this. But the question remains, what do you do once it is at max temperature (and max SoC) and can't evacuate additional heat fast enough into the air ? This is the equivalent of a diesel semi that cannot engage any form of engine braking - the loss of a clutch for example whilst out of gear, so conceptually a well known failure state. So far the best answers appear to be the same for the Tesla Semi as for any conventional diesel semi, i.e. creep carefully at low speed on the friction brakes, or find a gravel run-off. The only advantage the Tesla Semi has is that it can drive around town (yes, some towns and cities are on the top of very big hills) burning the SoC off below 100% until such point is at can make the descent safely.
I imagine that the people who race semi-cabs will be all over this quite soon. Surely some of their races start at the top of hills ? We know that racing BEVs quite quickly exposes the limitations of the different thermal systems in the various cars/etc out there.