thats what i think 2

but most people just laugh and say Saxony did not have a chance in h@ll at surviving...
Saxony did not have a chance in hell at surviving as long as the Empire was dedicated to subjugating it. The POD would have to be in the remarkable persistence that Charlemagne showed, not the resistance of the Saxons. That shouldn't be too hard, though - Charles did retreat in other places where he got himself a bloody nose. There's been a bit of speculation why he was so hellbent on reducing Saxony - wounded pride, traditional enmity, Christian missionary impulse, a sense of betrayal - and depending on which one you want to go with, you can shape your POD accordingly. Maybe the Franks could lose a couple dukes and counts and Charlemagne goes away, or other opponents prove more troublesome (the Agilofings or the Lombards are good candidates). A concerted 'Southern' strategy could be interesting. Charles decides after conquering Lombard Italy and reasserting control over Aquitaine to round out his control in that directiopn. He takes over Agilolfing Bavaria, pushes into Benevent and Spoleto, squares off against the Caliphate and maybe moves harder and earlier into the Balkans while leaving Saxony as a sideshow which he contains and keeps on the back burner.
Later on, the idea of Danish intervention is a good one. The Danes were supporting Widukind and they were concerned about the Frankish encroachment. Concerned, but not scared - they could give him a really hard time..