Someone will probably correct me with doom and gloom, but there's a chance there will be a continuation of sorts, they just wanna get away from the 4koma comedy style or something.
Wataten Shippuden let's go!
Maybe yes, but I don't see them changing the 4-koma format, nor do I think they need to end the series if they wanted to do that (every chapter has a bunch non-4-koma pages anyway). If we get a sequel, I think this ending is more so the author can have a break before the middle school phase.
Or maybe Hana will get into her rebellious phase and the title will change to A Devil Flew Down to Me.