Quite simple. The Czechs would've fought hard. They weren't strong enough to stop the Wehrmacht of course, but they were strong enough to bloody its nose. The Poles were much more effective than history tells us, I might add, because the Soviet invasion is what brought the, ahem, hammer down. They would've lost either way, of course, but they did a much bigger number on the Wehrmacht than we often admit (25% of the Luftwaffe destroyed). The Czech army was smaller but still comparable, in well established positions, with plans running back to the 1920s laid out. The Polish deployment was rather shabby, being too close to the border in open country and without sufficient mobile reserves or complete mobilization. I think we can expect around 5 weeks, like in Poland, to take out the Czechs.
The question then is is the Generals plot successful? If the Wehrmacht got bogged down, almost certainly I think. But a properly planned Fall Gruen that takes down the Czechs quick would've been a miniature battle of france moment, where Hitler is seen as a genius and the Wehrmacht unstoppable. But the 1938 Wehr was not the 1940 Wehr and afaik, the Luftwaffe was still pretty weak.
The problem here is that the Allies are rather useless. IF they ramp up mobilization and they attack, they can do wonders but clearly they were too weak mentally. Gamelin would've made a mess out of the invasion too. The Allies still had a lot of lessons in warfare to be learned, so probably the 38 Wehrmacht could hold the border if it defeated the Czechs.
There are other wild cards too, such as the Poles. These need to be discussed.
But let's get real guys.
