So there wasn't a fight to the death between Uhtred and Leofric. Instead, the vikings came into Wessex and took over. Luckily, Alfred and his family made it out alive as well as our hero and his companions.
They escaped into the marshlands to hide out until they could come up with a plan. Alfred was also dealing with the possibility of his newborn son dying. Prayers won't helping, but Iseult knew of a way to save him, but it meant the death of another newborn child. Saving the son was more important because he's the sign of Wessex prevailing. The child lived with the help of Iseult.
Alfred came up with a plan to have one big battle to end this once and for all, but the only way to do that was to get all the vikings in one single place. A bunch of ships showed up near the marshlands and Uhtred came up with a plan to use the marshlands against them. The vikings were killed and the ships were set on fire. The rest of the vikings will go to Wessex to join the other vikings. Alfred now can have the battle he always wanted.