The Blackcap in my garden has been singing since spring, but now stopped. Why? Did he migrate? Is he dead? Did his young become independent?

A blackcap bird is a migratory bird.these birds are in the state of least concern so you could see another blackcap.

Aerovan,
What do you mean by "state of least concern"? Is that an ornothological term?
I do not think blackcaps migrate in mid-summer.