The original question asked whether the allies could have advanced deeper into Germany in 1918-19. By the early days of November 1918, the German Army was retreating but not routed and it was as much the internal convulsions that provoked the end of the fighting.
They could have held the Rhine for a time. Trouble was, once Austria/Hungary folded, their southern border was wide open, so that an army on the Rhine would be outflanked by Allied forces advancing through Bavaria. All in all, they were surely right to cut their losses.
In fact, there's plenty of evidence that newly-installed revolutionary Governments facing foreign invasion are surprisingly adept at mobilising forces against the invader and protecting the new-won revolution.
If you mean Russia, I don't think the situations are comparable. Russia was just too darned
big for the armies of intervention to do much more than nibble round the edges. Germany didn't have that advantage.[1]
Revolutionary France is a slightly better parallel, but in 1792 France hadn't had a major war for nearly 30 years. Their involvement in the ARW messed up their finances but didn't involve much of the population in any fighting. That's very different from the German situation in 1918, all but collapsing after four years of carnage.
Incidentally, I think much the same about Lord Milner's notions of fighting on in Africa and Asia after losing the European war. I don't think the government could have sold it to the British public. For the past four years they had been fed the line that the fate of humanity was at stake in the battles of the Western Front, and had anyone now said "Well, it's not
that bad
. We can just fight on overseas," this would have raised the question "Well, if the front didn't really matter all that much, what exactly did our son get killed for?" in about half a million variations. And the seamen, many of whom had been doggedly putting to sea again and again after having been torpedoed three or four times already, might well have had something to say about being expected to go on doing so for this or that slice of tropical Africa. I can imagine an attitude analogous to the French mutineers "If they invade England, we'll fight 'em to the death - but not to hang on to a few colonies.They ain't worth dying for". If I'm right, that just leaves the US (and maybe Japan) in a naval war with Germany for a while longer, but finally resigning themselves to making peace.
In short, I think contemporary opinion was about right in viewing the 1918 battles as decisive.
[1] Istr a remark by General Max Hoffman at the time of the Spartakist rising in Jan 1919, along the lines of "If they seize power, the Entente will occupy Berlin. I wouldn't welcome that, but at least it's insurance of a sort".