God heals amputees in two ways, one in the present and the other in the future. One is by leading smart men and women to develop innovative prosthetics and other means to make amputees' impairments less disabling.* The other, if prophecies in Isaiah, Revelation, and elsewhere are to be believed, is by describing his plan to resurrect the dead into rebuilt bodies to fix up the earth during the millennium after Armageddon. These rebuilt bodies would have the limbs needed for the job. This second bodily healing doesn't happen prematurely because God is busy illustrating a point to Satan.
* An "impairment" is a problem in body function; a "disability" is the consequence of an impairment on activities of daily living.