Whether an employer's revokation of an existing accommodation is lawful depends on a number of factors, including the specific reasons behind that action, whether alternative, effective accommodations are available and are actually offered to the employee in question and whether there is some change in the employer's operation or the employee's medical status that would justify this change. Each situation must be evaluated individually in light of its unique circumstances to determine whether (a) a compromise between the employer's new goals and the employee's needs can be reach, and if not (b) whether there is sufficient evidence to puruse a disability discrimination case against that employer.
In these types of situations both sides should consider avoiding impulsive decisions as such termination of that employee or quitting the job by that employee. Instead, the parties should first explore the issue and see if they can reach some kind of compromise that works for both the employee who needs and accommodating and that employer.