The key broke off inside my Abus GRANIT CityChain XPlus™ 1060. A new one is $250 but a new quality padlock (went with Paclock) is $60, so I spent a while Dremeling through the lock's case to extract the captive link. It did not reveal a way to remove the key core.

The plastic case pops off easily.

Why do you need to remove the core? You just want to reuse the chain, right? Looks to me like you're already where you need to be.

I may not be fully understanding what you're after.

The best would have been to get the core out non-destructively and extract the broken key. 2nd best would have been to learn some hidden catch or screw I didn't see before, in case there's a next time. But yes, ultimately I did get the chain loose, and also confirm there wasn't some other way I had missed of getting to the core.