Clean sweep?

I had to stop writing about Sally and Gus in Sally's Blog because the characters were taking up too much space in my head. Since I batted them out of the way a little I've begun, at last, to have ideas for a new book. Last Friday I began some rudimentary plotting and the book has been simmering away all weekend. I've just opened up my planning file to do some more work and what do I see? The names of Sally and Gus. Yes, there are the names of the two new principal characters at various points on the page, but when I have added notes throughout, it's the names Sally and Gus that appear. Bah! Should I definitively kill the reprobates off somehow - maybe on Sally's Blog? Or should I give in and make the next book about them, a sequel to Plotting for Beginners perhaps?