Widukind put together an alliance with Frisians and Wends, but even then he was soundly defeated in 785. Historically, we know he surrendered and accepted baptism for himself and his people in exchange for peace. For this much, he was beatified. His circumstances before and after his surrender, however, are the subject of legend and speculation.
Prior to his surrender, the legend says, he slipped into Charlemagne's camp, disguised as a beggar. He got swept up in the crowd that was attending Mass, but instead of seeing the priest consecrate bread, he saw him holding a beautiful child. As the faithful came forward, the priest gave the same child to every person. Widukind was so awestruck that he let his guard down and revealed the deformity of his finger to a soldier, who recognized and arrested him. During interrogation, Widukind described the miraculous vision of the child. Thus were peace and baptism negotiated.
Following this peace, Widukind drops out of the contemporary annals. Historians speculate that he was sent to the Reichenau Abbey, one of the monasteries in which Good King Chaz imprisoned deposed enemies. Of course it is also possible that Widukind was allowed to remain in charge of Saxony, or some part of it, as a vassal of King Chuck. Later legends that he was a great builder of churches might support that claim.
The big idea here, I guess, is politics. Charlemagne was forging a Christian empire, and even if Widukind saw the Christ Child in the Eucharist, the rest of the Saxons did not. And yet, they all received baptism, with King Charlemagne as the godfather for each and every one of them. Faith? Probably not in every case. Pragmatism? Certainly. Corruption? Eh, it's better than perpetual war.