Ironically, the concept has been in effect for several decades, but under a different cover.

Initial military enlistments and officer commitments bring with them a period of active duty, followed by a reserve period (active and/or inactive). During that reserve period, folk have found themselves called back to active duty.

When career military folk retire at less-than-thirty years service, that delta period between retirement date and thirty years is a reserve period during which call-up can occur. Also, a person must "request" to be placed on retired status, and a decision as to when that date shall be is subject "to the needs of the service."

Joining the military brings with it a quantum of risk - physical and chronological. It's just part of the profession.

Not having "stop-loss" brings a very interesting military management question - would not having it result in such a personnel management risk as to require activation of the draft?

There just is no perfect solution to answering a response-based problem.