In OTL the Battle of Heavenfield had been lost by the Welsh, led by Cadwallon ap Cadfan, to the Northumbrians, led by Oswald of Bernicia. Oswald of Bernicia then went onto reunite Deira with Bernicia and he became the King of Northumbria.
But WI the Welsh hadn't lost, hadn't suffered substantial losses and had actually killed Oswald, rather than Cadwallon. Would the Welsh have continued into Northumbria with Mercia and taken it, and carved up what is now England between them? If so would the Welsh and Mercians have had anymore luck in repelling the Vikings? Would the Welsh dragon ever come into existence?
But WI the Welsh hadn't lost, hadn't suffered substantial losses and had actually killed Oswald, rather than Cadwallon. Would the Welsh have continued into Northumbria with Mercia and taken it, and carved up what is now England between them? If so would the Welsh and Mercians have had anymore luck in repelling the Vikings? Would the Welsh dragon ever come into existence?