I had two cases of structual breakdown as of now on a vintage KTM bicycle:

1. The right half of the handle broke off while I was mid traffic, gladly I could recover from this without falling since the left part was still firmly attached

2. The crankshaft broke off on one side with a sharp edge of greased up metal slicing into my leg, this happened on a bicycle lane when trying to accelerate from standstill.

I am still riding the same bicycle, I just had used it a lot back when those things happened and as a student I didn't really have the funds to maintain it properly when somehing made a creaking sound.

Regarding your 1) Easy peasy! Imagine accelerating out-of-saddle (Wiegetritt) from around 45kph to intended 55 to 60, to get through an underpass fast, to get ahead of traffic, because wanting to cut the sharp curve at the end and have enough speed for effortless uphilling.

Crunch-Bang! Got my handlebar including the stem painfully into my chin. Guess what? Astonishingly (to myself) I did NOT fall, but managed to wobbly and swayingly brake to standstill, by the still attached brake wires, evacuating to the small sidewalk, and pushing it out of the underpass.

There https://maps.app.goo.gl/D26VGpXXZ3TJmbGTA from left to right.

I think it was a good thing to be ahead of traffic, and not between/beside it in that moment.

Even more funny, at that time there was a large bicycle store only a few 100m away, so I got a new stem in about half an hour, while calming down a little ;>

2) Yah, thats ugly. Almost tore up my ankle that way, but luckily it was only a deep cut, which took 2 to 3 weeks to heal.

Otherwise? Torn chains, mostly.