No one was locked in. You know what the Japanese anime industry does in this case? Sometimes, they draw out the story, so that entire episodes are taken up with just powering up. (Dragonball Z) More commonly, they just wait for the author!
Of course, the anime industry has the advantage, that the "way someone is drawn" can remain the same after a gap of 5 or 10 years, while human actors age. However, in 5 or 10 years, I don't think that's going to be prohibitively expensive anymore.