Sorry to hear what happened to you and the bike. Lucky you no real bodily harm done.
I went wide on a decreasing radius corners a few times initially with the z650. What I did just stand up the bike and slam the brake hehe. Mine has ABS so no issues of locking the tires.
When taking corners aggressively (In my case aggressive probably is mild to other people hehe) ;
1. Make sure at least initially have your head a bit on the side of the bike into the direction of the corner and bent the elbow a bit.
2. If you feel lean angle not enough and it seems you are going wide, bent the elbow more pointing it downward and at the same time push the handle for more counter steering.
3. Items 2 should naturally lower your head, shoulder and body into the corner.
4. Putting out your knees will come naturally. I am not a speed demon at corner where I need to slide half my ass off the seat.
5. Maintain throttle. If you reduce throttle too quickly the bike tend to stand up and you go wide.
The z650 probably can handle most corners. I think the ABS version of z650 is one of the safest motorcycles.