AT 1605, THE FLT CALLED BLYTHE FSS STATING HE WAS 25 MI EAST FOR LANDING. WHEN HE HEARD THAT HIS BUSINESS ASSOCIATES IN ANOTHER ACFT WERE PREPARING TO DEPART BLYTHE FOR TWENTYNINE PALMS, THE PLT CANCELLED HIS LANDING INTENTIONS & STATED THAT THEY WILL BE GOING ON TO TWENTYNINE PALMS ALSO. THE PLTS IN THE OTHER ACFT WERE ON AN IFR FLT PLAN & STATED THAT BECAUSE OF SOLID INSTRUMENT FLIGHT CONDITIONS THEY DID NOT HAVE AN OPPORTUNITY TO LEAVE THE ATC FREQ TO COMMUNICATE WITH N200WJ. THE ACFT CRASHED IN DESERT TERRAIN 32 MI EAST OF TWENTYNINE PALMS. A WITNESS STATED THAT VISIBILITY AT THE ACCIDENT SITE AT 1630 WAS LESS THAN 1/4 MI WITH MODERATE RAIN. THE PLT DID NOT HAVE A MULTI-ENGINE OR INSTRUMENT RATING,AND HIS CLASS II MEDICAL CERTIFICATE HAD EXPIRED. THE PAX HAD UNDERGONE DOUBLE BYPASS SURGERY IN 1975 FOR SEVERE OCCLUSIVE CORONARY DISEASE. THE AUTOPSY INDICATED THAT THE BYPASS VESSEL HAD A FRESHLY PROPAGATING CLOT, TOTALLY OCCLUDING THE LUMEN.