The Heptarchy was never totally divided. There were periods where one of the kingdoms dominated quite a few of the kingdoms at certain points. First it was Northumbria, then Mercia, and finally Wessex. They weren't at all balanced. It was simply a number of factors that left Wessex to eventually unite the kingdoms together, largely that the Danes kicked the crap out of everyone else. Remove all outside factors, chances are still good that one kingdom would at some point achieve dominance. You'd just likely see a more regional focus to some degree, closer to France where the Dukedoms were practically kingdoms only nominally under the control of the crown.