Most of the time it’s not a question of whether or not to replace a motor. By the time a contractor is called to the scene, the motor has already failed or is in its death throes.
Replacement is usually a viable solution, because repairing a motor can be fairly expensive. Indeed, it may be the case that the cost to repair the motor in a typical air handler (15 to 40 hp) is greater than the cost of a new motor.