It is expected behavior that a page would no longer be available after its "Publish to" date is reached. I just double-checked the scenario in Kentico v10.0.51. However, there's a few things that could affect this.
Are you still authenticated when testing this? If you are using a browser that is already authenticated as an editor, then you have permission to view expired pages. Have you tried viewing the page in an Incognito window?