MK Airlines dont seem to be doing so badly with their 742's. They are flying huge volumes at near capacity.
Have cargo will fly, some legs pay better and some just to subsidise positioning to next good load.
Cargo southbound out of Europe to Africa pays up to three times better than over same leg northbound, but notwithstanding still makes good economical sense even with a 742.
Even DC-10's and DC-8's can still make money from Europe to Africa if they limit their flights to the equator region and then some cheap return cargo.
IMHO there is much latitude still for good reliable 742's.