Motor powered on and brakes disengaged for three days, should I be worried?
There is a very high chance you have demagnetized the rotor. 

Permanent magnets have something called Curie Temperature: http://en.wikipedia.org/wiki/Curie_temperature

If you take a magnet to its specific curie temperature it will lose its permanent magnetism.

It can easily be checked by backdriving the rotor of the motor at a given speed and measuring the terminal voltage that is generated. 

You should have the machines voltage constant \$k_e\$ to then calculate what the voltage should be via:  \$V = k_e\omega \$  (careful about how \$k_e\$ is defined, peak phase or peak line-line).

I haven't personally demagnatised a machine like this, but a technician on a project of mine did when they forgot to disengage a poweroff brake (slip torque around 30Nm) and accelerated the machine from 0rpm to 10,000 over 30seconds on a rig that could generate in excess of 30Nm at 10,000.