Yes, some kind of Czech and Polish autonomy would be a must but Germany would not accept after an unexpected triumph of Fall Gelb.
Much different situation though if Fall Gelb fails and the Western front turns into a stalemate. I see much better chances for a negotiation in that case.
Look at this point Britain has already failed Czechoslovakia, Poland, Norway and to some degree France, Belgium, and the Netherlands. If they quit at this point they lose so much international prestige that they cease to be a major player anymore and the empire itself might be shaken. Don't forget Britain has owned a huge empire at this time and any show of weakness or defeat might compromise the whole thing. And Germany was in too good a position to consider any proposal which would have been acceptable for Britain like reinstalling Czechoslovakia and Poland to some degree and abandoning Denmark and Norway.
What's ironic is that after winning the war... The UK ended up losing its empire almost immediatly and ceased to be a great power. Also Poland was not liberated
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