I don't deny this possibility in my personal theory. But to me, it still involves a contract, hence them going on hiatus, because they can't stream without a contract, whereas Mysta and Nina knew they were graduating in advance, not trying to last minute re-negotiate.
It's also a surprise to the rest of the boys, so to me it still makes sense they believed they would come back, just that the re-negotiation was taking a long time.
But tying it back to your theory; it's possible that Cover wanted them out, so they imposed stupidly high demands on the boys by contract, so they walked when they saw Cover wouldn't budge. (But then, why would Cover pay tens of thousands of dollars to buy Vesper a new model and give Magni a 2.0)