If you're selling your project, then public release is actually just the halfway point in the project's life. There will be a lot of feedback, bug reports, fixes, and patches to figure out. Players will expect maintenance and updates. If you manage it well, you might be able to relaunch the game again and again, and cultivate a healthy "long tail" of revenue over time... but if you're making a commercial release, hopefully you're not seeking business advice from a level design book, so we'll just stop here.