A returning veteran who meets the requirements of this subtitle shall be reinstated: to the class previously held by the returning veteran within the principal department or other independent unit in which the returning veteran had been employed; or to a position of equal responsibilities, qualifications, and rate of pay. If, because of a disability sustained during service in the uniformed services, a returning veteran is not qualified to perform the duties of the position that the veteran previously held, the returning veteran shall be reinstated to a position that: has duties that the veteran is qualified to perform; and provides the rate of pay, seniority, and status that are the same as or as similar as the circumstances of the case allow to those of the position previously held by the veteran. Subsections (a) and (b) of this section need not be implemented if the circumstances in State government have changed to the extent that implementation is impossible or unreasonable.