But the guarantee wasn't granted only because of Hitler's invasion of Czechia - it only speeded it's declaration, as joining the franco-polish alliance by the UK was already considered in London since Munich. Of course if without Czechoslovakias termination Hitler declares some demands on Poland, the West still would want to appease him to buy time, but if Hitler decides to go to war, the West would still declare it on him, guaratees being granted or not.
Unlikely. Before German invasion of Czechia, appeasement still remained the default foreign policy approach towards Germany. That invasion was the event that radically discredited it, by showing Hitler was deeply untrustworthy, and his expansionist foreign policy went much beyond irredentism for ethnic Germans.
The objections about the economic motivations that drove Hitler to invade Czechia make sense, and in his view, the Munich settlement had only deprived him of the opportunity to conquer all of Bohemia-Moravia. Nonetheless, a PoD may be reasonable where he opportunistically decides to delay the annexation of CZS in order to keep the Western powers content with German foreign till Poland is dealt with.
I'm not entirely sure if German economy can afford to delay the annexation of Czechia till late 1939 - early 1940 if rearmament is not toned down (something Hitler would be unwilling to do given his plans for a war against the USSR). But if it can be done, it is possible that a slightly more cautious Hitler may do it. After all, after Munich CZS had already become a satellite of Germany, the status quo gave Germany some substantial economic and political advantages, even if nowhere so extensive as full-fledged annexation.
It also depends on what TTL Hitler actually plans to do with Poland. If he really wants total control of it to start its Lebensraum Germanization, in the end a war with the Entente would be inevitable. If he deems it enough to get satisfaction of German "reasonable" claims (Danzig, the Corridor, and Upper Silesia) and making Poland a satellite of Germany one way or another as an anti-Soviet strategic springboard, then he may gain that, either through a repetition of the Munich platform if Poland proves compliant, or a German-Polish war if it does not.
Or alternatively, one may get rid of Hitler altogether. Have Maurice Bavaud gun him down on October 9, 1938. The likely successors (Goring or the Heer) were so fearful of a general war with the Entente or the USSR that they would heed the Munich status quo and only press a "reasonable" German irredentist agenda against Poland if the Entente powers remain tied to appeasement. Since they did not want a general war, they would be willing to slow down the pace of rearmament to stabilize German economy, which makes the plunder of Czech wealth unnecessary.