Well, unless you've declared a war, (or the UK is in a faction with the Czechs) the UK will accept Germany taking the Sudetenland ~94.5% of the time.
If France is not in a faction with the Czechs, they will then follow the UK's lead and allow Germany to take the Sudetenland ~97.2% of the time
Czechoslovakia then has a base chance of rejecting of ~4.5%. This will increase if any of the following hold:
- Austria still exists (increases rejection chances to ~11.1%)
- Czechoslovakia has at least 75% the army strength of Germany (will ALWAYS reject)
- Czechoslovakia leads a faction (will ALWAYS reject)
- Czechoslovakia is in a faction (increases rejection chance to ~78.2%)
- Czechoslovakia is a puppet of a nation other than Germany (will always reject)
Do any of the above apply?