I think Russia will "win" many battles but they cannot prevail in the war, and have no chance of either conquering, or maintaining political control of the whole of Ukraine, unless extreme measures are taken.
Unless Putin is removed, and even then I don't see a suddenly pliant Russia, they have to and will make concessions.
The question is how Russia can be given a way out to end the conflict but feel that something has been secured on their side, to justify an end to hostilities.
I thought initially that Putin would seek to establish a bridge between Crimea and the DNR/LNR, hence the current concentration there, and maintenance of that may be their bottom line as time drags on. Currently I cannot see that as being acceptable to US/EU/NATO so its very difficult to see how things will pan out.
This, in spades. It seems fairly clear that Crimea, Donbass and an unbroken chain of territory linking the two is the absolute minimum that Russia is looking to seize permanently.
I suspect Putin was planning to take Kiev and absolutely everything east of the Dneipr, then "magnanimously" announcing a ceasefire. The Dneipr makes for a fairly significant strategic barrier, to satisfy misplaced Russian fears of a NATO conventional assault, and his commanders will have anticipated that Ukrainian troops would blow most of the bridges as they retreated, making it a more defensible barrier. It effectively cuts Ukraine in half, and the strategic value of Crimea, both militarily (provides year-round deepwater port for Russian fleet) and industrially (confers control of territorial water, therefore ownership, of areas of significant oil and natural gas reserves) is firmly established.
Ukraine will obviously want the return of every inch of territory seized by Russia since 2014, plus total reparations for the massive amounts of damage to roads, infrastructure, cities and everything else, plus the thousands of murdered civilians. As negotiations go, it's hard to see any common ground where either side is going to be happy to compromise.