I pretty much play until an inevitable ending rears its ugly head, then my friends and I generally play out the biggest impending battles just to see how they would’ve gone, or to see how large of a chunk inevitable loser could take out of their foe’s force before falling.
The fact of the matter is:
If SU falls and UK or US aren’t in France or Italy with a complex or set up to take Germany before Germany’s next turn, then Germany outproduces the UK and wins.
If UK falls, the SU can’t hold Germany alone, and either the US goes to Europe and gives Japan free reign to send hordes of tanks into Russia, or they leave the Soviets to die alone.
If the US falls, that’s good game anyway.
Playing out to every last city is wholly unnecessary, since most of the time to get close, you basically get into a position where the end result is clear a full 2-3 turns before it would occur, wasting everyone’s time unless its a guarantee for multiple epic clashes.