There are a few 747-100s and 200s still flying in the freighter market, how many, I don't know, but, yes, they are slowly fading into the sunset.
There are a few very dodgy operators flying them in SE Asia right now, and JAL still flies a few.
The ones we got in '89 were already 15 years old and had 15,000 cycles on them. Parts fell of on takeoff, I was on a flight where the gear punctured the fuselage...
Same goes for the DC-10, its become a rareity as well. The MD-11 does great for cargo though.