Kaputt gave me so much trouble when I had to understand that gestorben means "[have] died" ... I was not expecting that! German, like ancient Greek, has so many specific words for things.
Dative and genitive cases are totally gone, because it has been 20 years since I seriously paid attention to the study of the language... not much chance to use it, other things came along that demanded my attention ... until Covid-19. But, once upon a time, I could actually think in German, and occasionally - when I am listening to German lieder, for example -- it comes back in big flashes. This is why doing the translation work is so interesting to me on such songs ... my limited vocabulary can reconnect to what I used to know and connect with things I never learned in university.
RE: "Ich bin der Welt abhanden gekommen" -- my current situation (more or less)!