PLT AND WIFE HAD FLOWN TO DALLAS (ADDISON ARPT) AND SPENT EVENING WITH FRIENDS. RETURN FLT INITIATED AFTER MIDNIGHT INTOLOW CLNG AND DRIZZLE, ABOUT 12 MINS LATER, WIFE CONTACTED DALLAS (LOVE FLD) TWR ON EMERG FREQ 121.5 AND REPORTED PLT WAS SICK AND UNABLE TO CONTROL ACFT. TWR COORDINATED WITH ARTCC FOR RADAR ASSISTANCE AND ATTEMPTED TO VECTOR THE ACFT TODALLAS-FT WORTH ARPT (DFW), ABOUT 4 MILES SOUTH. WIFE REPORTED 'CAN'T SEE A THING.' FOR APRX 18 MINUTES EFFORTS TO BRINGTHE ACFT OVER DFW CONTINUED, WITH ARPT LIGHTING AT FULL INTENSITY. ACFT WAS INSTRUCTED TO MAKE A SHALLOW LEFT TURN TOWARD DFW AND RADAR CONTACT WAS LOST SHORTLY THEREAFTER. INVESTIGATION REVEALED ACFT COLLIDED WITH TERRAIN IN A NOSE LOW, LEFT-WING-DOWN ATTITUDE. AUTOPSY (PLT) SHOWED EVIDENCE OF TWO PREVIOUS MYOCARDIAL INFRACTIONS AND SEVERE OCCLUSIVE CORONARY ATHEROSCLEROSIS. RELATIVE REPORTED WIFE HAD A FEW HOURS OF DUAL FLT TIME BUT WAS NOT A PLT.