Weimar Republic died (believe it or not, but from completely natural causes) and was replaced by Nazi Germany (i.e. the Third Reich) for one and only one fundamental reason.
It failed to protect Germany (and the whole Western civilization) from being attacked, invaded, conquered and destroyed by the Bolshevist Soviet Union. And subsequently transformed into a global Communist state – Union of Soviet Socialist Republics.
It fundamentally failed because to win the genuinely existential war with the Bolshevist Soviet Union (a very powerful military, industrial, political and social system specifically created for but one purpose – conquering the entire world), you had to have an even more powerful system.
The liberal-democratic system of Weimar Republic (or of any other Western democracy for that matter) was simply not powerful enough to win the existential war with the Bolshevist totalitarian system.
Only the Third Reich was. Consequently, the disgraceful demise of the Weimar Republic and its replacement with Nazi Germany was totally and completely natural. And vitally (existentially even) beneficial for Germany and for the whole European (and Western) civilization – despite the exorbitant, horrific and mostly unnecessary cost.