All this has happened before, and will happen again.
In performing a grand rewind, Bill has reset his story to the beginning, though he retains his memories of the previous timeline where he, Tom and Gloria had traveled to the future.
But as with all stories, the beginning is a road to limitless adventures, and the Stone has proven to change things in unexpected ways. From this moment the timeline could repeat itself, or it could veer off into new and uncharted territory and new adventures. He still has no idea where the Ahn'Ger Stone came from and only a vague idea of how to make it work, but it is within his power to change or embrace whatever destiny it has in store for him.
Below are the three potential timelines that could have occurred at the moment Bill discovered the stone. Remember that with his knowledge of the past, these timelines will be FOREVER changed from their original paths, and can change into new adventures.
Lover's Knot: Tom or Gloria appears across the road, waving Bill over exactly as they did before.
Diary of a Stoop Kid: Bill's day of reckoning with the bullies has arrived.
Family Matters: Bill is interrupted by his sister Kimberly, or one of his parents.