There is little downside to inactivation of a license or letting it expire on its own. Every hospital or surgery center in which you seek privileges, many insurance companies, and every new state where you seek licensure will perform primary document source verification regardless of whether the license is active or not. Limit the number of states medical licenses where you practice in order to avoid having to fill out scores of pages of past and present licensure queries. I cannot imagine being a locum tenens with licenses in 40 states.