Zundapp came back in the late '40s with the "Elefant", their factory-built combination powered by a big flat-twin. This lasted into the late '50s, but Zundapp didn't continue for-stroke development much, instead put all their efforts into two-stroke commuters and mopeds. They still exist, and Zundapps are "quality" mopeds and learner bikes on the European mainland.
The GERMAN Triumph company - actually, the British company was a offshoot of IT at the start of the 20th century! - eaked out a living making domestic tinware after the war (when I was a kid, my primary school canteen had big Triumph aluminium pans LOL the name must have stuck in the forebrain until I made the mistake of watching The Great Escape!) but later went into of all things typewriter production! I think they lasted in this until the very late 1970's but didn't move over to the production of wordprocessors etc. like so many typewriter companies did to carry them into the PC age. Adler went back to producing motorcycles, along with of course NSU - I forgot about them!!! - producing a beautiful range of two-stroke twins while NSU specialised in fourstroke performance singles; NSU single-cylinder 250s and 350s were class leaders at a time, both on the road and on the track. NSU went into cars for a time, but both companies' motorcycle production died in the face of the 1960's Japanese onslaught.
As for Puch....
they went back to their field of expertise VERY quickly - small two-strokes up to 125cc - and as well as rivalling Zundapp, Kriedler etc in Europe in the sales of 125 sporty two-strokes....were the first company in the world to take the stylistically-brave but OH-so finacially rewarding step of...putting a shopping basket on the front of their 50cc mopeds...and the rest is history. You meet the nicest plagiarists on a Honda! LMAO
"Well, my days of not taking you seriously are certainly coming to a middle." - Malcolm Reynolds