To illustrate my point.
1 - Jorvik is quite well placed, as OTL. Far from direct threats, being a sure door to Scandinavia and North Sea trade. I don't see any reason that, without Wessex resistance happening as OTL, they won't still be the power in the Northern England.
2 - With all Mercia conquered, things can evolve very differently. Jarldoms turning independent, recognizing partially or totally Jorvik authority. I would think the first solution is most likely, however.
Giving the Danish forces in presence, however, it would turn quickly to an Anglo-Dane mix if independent or an easy prey for a united Wessex. Actually, maybe its top priority.
A Jorvik Mercia however could both nerf the kingdom, making it the main power in Middle England, but would make it harder to manage, more anglicized.
3- Northumbria, in the case of a strong Jorvikn would probably know the fate of Mercia under Wessex rule : client state eventually absorbated.
4 - East-Anglia is kind of stuck in a strange position. The Danes there already turned to Anglo-Danes quite quickly. A bigger East Anglia could turn powerful, and while Wessex is busy in Mercia protecting his b...borders, an East Anglian king could protect his own and even manage to divide Wessex by taking/Clientelising Kent (5b) and Sussex (5a) (the sons of Alfred not really fond of "brotherly affection", it would be somewhat easier after the PoD.
Eventually, tough, their anglicisation would turn against the ruling part, and you may end with an Anglo-Saxon (maybe mixed with Dane) family on throne eventually. Or a suspiciously AS looking Danish king, that would make an agreement with what remains of Wessex against Mercia/Jorvik.
5 - Wessex is in a relative bad position right after the defeat, and a civil war and/or another defeat in Mercia could seriously hurt the kingdom. However, it does have the number, the legitimacy and as long it manages to have divided ennemies, a relative unity.
At worst, it's shattered and a Danish jarl or king takes the crown.
Eventually, even in the case of a Viking victory, an Anglo-Dane society is most probable to emerges, clearly more AS than was Anglo-Norman society. The conflict would be resolved quickly, one way or another, as there's no real infrastructure or big armies to length ennemies.
For trade, Anglo-Dane kings would probably continue to support the existance of southern trade centers along previous lines as they did AS Kings and OTL south Danes.
A total Danish victory would see, IMHO, the emergence of 2/3/4 states : Jorvik, East-Anglia, Mercia, Wessex, possibly shattered.
Without Wessex reemergence, I don't see any sooner an united England.