I don't see how a warning of impending abandonment makes it no longer abandonment. What if the client needs 6 months to climb out of an addicted/regressed/fragmented state, created by therapy, and ending in 1 month will drive them to a nervous breakdown? Oops.

The therapist can do whatever they want. But having a good reason for leaving someone high and dry after mooching their money and trust... it's still leaving them high and dry. And then the client is supposed to start over with a new therapist, and risk repeating the same nightmare.