Another factor, is what state the Russian military is actually in. Impossible for any of us to tell with any certainty, but if European nations felt, based on worthwhile intelligence, another year or so would make a material difference then I would say there would be far more stomach for that than anything that extended much beyond that.
As well as shifting US policy, albeit temporarily, the deployment of North Korean troops could be a catalyst for a notion of one more push from Europe if US support falls away. If it was felt there was a discernible and worthwhile endgame within 12 to 18 months, as that would make economic sense.
Obviously, the above is all predicated on Ukraine rejecting any putative ‘deal’ as posited by Peston.
There are so many variables in this. Always has been, but Trump being elected has thrown a fuck off grenade into the mix.