There are a fair number of PICs with QEI modules. If your PIC has one it could be connected to two of the sensors (which will produce a somewhat skewed signal but near enough to quadrature to work), and that would not only tell you if it is running with minimal software intervention, but how far it has turned since you last polled it, eliminating the possibility of a motor with a jammed drivetrain or controller fault that is vibrating through a small angle being misdirected as running.
However as I said earlier, the real expertise for solutions that are internal to the PIC is over at Microchip's forums, and to give you better advice, we need to know which PIC and any peripherals you've already tied up for other purposes.