^Well, look at it this way: if the books had been halted at an earlier stage, we wouldn't have gotten paid for them. So it could be worse.
And I've written tons of stuff that never saw print. Every writer does -- it's part of the learning process. So you get used to it. You chalk it up to experience and move on to the next thing. And you keep the unpublished stuff in a drawer (or these days, a directory on your hard drive) and maybe get to cannibalize it for ideas later on. Although that's probably not a good idea in this case, since there's a chance these books may still see print eventually.
And I've written tons of stuff that never saw print. Every writer does -- it's part of the learning process. So you get used to it. You chalk it up to experience and move on to the next thing. And you keep the unpublished stuff in a drawer (or these days, a directory on your hard drive) and maybe get to cannibalize it for ideas later on. Although that's probably not a good idea in this case, since there's a chance these books may still see print eventually.