Well, beat a boss. About a second later, the bosses delayed attack beat me.
On the plus side, it remained beaten. And after I died, I became alive again.
On the minus side, as a consequence of things being missed, I spent almost exactly an hour traipsing round the world trying to figure out where I needed to go next.
ZOMG Spoiler! Click here to view!
After killing the boss, you get teleported. Presumably to where you need to go next. However, I died as soon as I appeared, not seeing where I was to allow me to return.