Thanks for posting an interesting topic, Warspite. I am only now catching up. The late 1930s are intriguing as how the history as we now know it unfolded. So many moments where history could have taken off a different tangent. Or so it seems, at least. I especially appreciate your effort in keeping the benefit of hindsight out of equation.
Even towards 1939, that year included, the diplomatic undercurrents ebbed and flowed. Molotov-Ribbentrop Pact was a shock to the system as it deserved to be. A few saw Stalin and Hitler making a pact, but of course they did, for the reasons we now know, why wouldn't they? France and UK had failed to stem Hitler with a pact with USSR. At that moment, peace lost, war won. No going back.
But yet so many final pieces of the historic puzzle were not yet in place. After invasion of Poland by the two dictators, both Hitler and Stalin had significantly more leeway to plan and execute their deeds. Stalin went on to begin the annexation of Baltics, while Hitler was ready to attack France with the two happy chaps in an uneasy agreement to cast their mutual situation aside for the time being.
At the time of invasion of Finland by Stalin, there were still no larger alliance in place apart the loose Franco-British pact. Interestingly, when you look at the top foreign aid towards Finland during Winter War, three countries stand out. Sweden, for the obvious reason of preferinng to continue to have Finland as their eastern neighbour went to greater lengths than perhaps appreciated, including not declaring neutral in the war, just not a participant. Then, France and Itally. France, because Daladier wanted finally to show a strong line against communism, with local politics in mind in particular. Italy, because how Mussolini wanted to oppose Bolshevism. Relations with Germany and Italy hit a rock-bottom, and at this stage one could but remember the Great War and which side Italy took there, after procrastination. Eventually, their Abessinian adventures and the embargo that followed had perhaps not a little role in forcing Mussolinis hand and choosing to go war with Hitler, instead of being a passive (relatively speaking) bystander for a bit further.
So what if Finland would have waited a bit further, to see if the Franco-British expedition would eventually land in Norway (despite Norway declaring neutral in fear of Germany), and passed through Sweden (despite Sweden opposing the move), and actually arriving in Finland? Stalin, then, would have all of a sudden faced the two arch-enemies to global communism at a side-event as far as USSR was concerned. It did not happen of course, Finland was already beaten by early March 1940, Stalin just was not sure of that, as many pieces of front line sort of still held together. Instead, he called a truce, Finland agreed, Germany was agitated though, and invaded Norway a bit later to deny UK the access to Swedish ore.
To answer the original question, with no hindsight, and while trying to understand the realpolitik of the time, I can't fault Chamberlain. Sudetendeutsch was a negligible price for keeping the piece, if Hitler would have been subdued as the result. Of course he was never going to be subdued, as we know now. Also, Chamberlain and Daladier tried to build alliances, Stalin's USSR included, but it did not work out, at all. Lots of violent events toook place before Barbarossa. I don't blame Chamberlain for that. The two dictators mostly got what they wanted, until Hitler decided to go at USSR, declaring war on USA while at it, and the final pieces of history as we know fell into their places.