I'd just like to hear people's opinions and speculations. If Ulfric wasn't censured for the duel, what would have happened?

The Civil War would still have happened.

he still would have won probably
he used the thuum to pretty much show everyone else his power, not to kill specifically toryyg (sp)
the high king was young and inexperienced, a good few NPCs said so
and ulfric seems pretty combat/military oriented
so ulfric most likely wouldve won without the voice, but it left a bigger impact on the high kings supporters when he used it

That depends on Ulfric.

Under Skyrim law, there has to be a moot. If Ulfric was chosen as high king, Skyrim would undoubtedly declare independence and restore Talos-worship. If he was not, Ulfric would either return to Windhelm and resume his jarl duties, or he would challenge the new high king. Probably the latter, since his cause may be just, but Ulfric's primary focus is Ulfric.

I meant after the duel. If people accepted his win afterward, what would happen?

Probably so. I think the only way it could have been avoided is if Torygg declined the duel, stepped down as High King, supporting Ulfric's bid and independence from the empire in the moot. There would still have been dissent but the imperial jarls might have backed down if that happened. It would take a big man and even bigger Nord to be that humble, though, and Torygg wasn't that man.