Apart from the obvious fact that Wales wouldn't have a national assembly, policy would still be run from Westminster, and a lot of individual Welsh political career would be changed, I'm struggling to think of serious knock-on impacts. It would very likely kill off the slender support John Prescott had for introducing regional assemblies in England in Labour's second term, so there is that, and when Labour next goes into opposition it would probably consequently embrace a devolution-all-round package. With the distance Welsh Labour in the national assembly held from Westminster not being present, Plaid and the Lib Dems might do a little better in Wales in the 2000s. Tony Blair would have a bit less of a reputation as a demented control-freak without his attempt to ram-rod Alun Michael into the position of First Minister, and Michael would continue to have a serious career at Westminster.
So.. yeah. Not a lot.