Well, here's a thought:
Buy as many Thermodisc (
www.tod.com->Products->Bimetallic temp switches) "click-style" resettable temp sensors as you have motors.
Strap the sensors to the motors with tywraps. Wire them in series, and use a Mach 3 input pin...or wire them in series with the E-Stop pin.
If any motor gets too hot, it will open (or close...your choice at purchase) and trigger the condition.
When the motor(s) cool down, the Thermodisc will reset (re-click?).
Thermodiscs can be ordered for just about any useable temperature range, say open at 90C and close at 40C...etc.
BTW, I don't work for or have any interest in Thermodisc, Inc. My day job is EE, and I'm simply famiiliar with the product.
-Pat-