If the Allies actually dispatch forces to rump Czechoslovakia, they clearly mean business. The wave of guarantees probably comes at the same time, and Poland is likely to accept for the same reasons as in OTL. Germany presumably reacts by arranging a pact with the USSR. Europe is in the same situation as in August 1939: Germany's next action will cause a big war. But there is a significant difference: Germany does not have Czechoslovakia's considerable wealth and armaments.
As for Germany pulling a Munich 2.0 on Poland after grabbing the Sudetenland ...
Actually, Hitler really really wanted an alliance with Poland right until 1939. The only territories he demanded were Danzig and an exterritorial road across the corridor. So why did Poland refuse? I don't think anybody important in Poland had any illusions as to the possibility of resisting Germany on their own. But Poland wanted to remain neutral and independent as long as possible, and membership in the Axis would obviously impair Poland's freedom of action. It was therefore desireable to prolong the existence of the status quo as long as possible.
So Poland tried to buy time, exploiting Hitler's relative unwillingness to confront it and pretending not to hear when Germany enquired about Danzig. And Poland managed to get away with this until Germany defecated on the treaty of Munich and Britain reacted by terminating appeasement and issuing guarantees left and right. To the Poles it seemed that their strategy had been vindicated, and accepted the British proposal. Now, if Germany wished to attack Poland, it would automatically become embroiled in a war with France and Britain. Surely, the Polish foreign minister thought, plunging Germany into such a war was something no sane man would do. And most tragically, just like Stalin who knew that no sane man would attack the USSR before dealing with Britain, he was correct.
So I can think of two ways of having the Munich 2.0 happen:
1) Change Poland's foreign minister. Either replace him with someone more cautious, or better at understanding Hitler. Or cause him to realize that Hitler fears nothing and won't back down. So Poland gives away Danzig and an exterritorial road across the corridor and joins the Axis. Pterodactyl-sized butterflies ensue.
2) Germany proceeds to ask for the deal I described above before grabbing the rump Czechoslovakia, and insists on Danzig and Polish membership in the Axis. Britain and France remain in appeasement mode and declare they don't want to die for Danzig. As a result, Poland accepts. The million-dollar question is what happens next. Sooner or later Hitler will cross the line as far as Britain is concerned, and then there will be no reason not to issue guarantees left and right. Even if Britain won't fight just yet, some sucker who would otherwise have allied with Germany might just be prised out of the Axis, killing two birds with one stone by depriving Germany of an ally and giving it another front to worry about. Will Poland accept anyway? Or will it decide that since Germany currently has no demands against it, it would be unwise to tempt fate and that the best course of action is to watch events unfold?