THE PLT COMPLETED A 30 MIN INSURANCE CHECK FLT, THEN LOADED THE ACFT WITH BAGGAGE/PAX & DEPARTED DECAUTER, IL ON A FLT TO NAPLES, FL. A REFUELING STOP WAS MADE AT COLUMBUS, GA. AT 1750 THE ACFT DEPARTED COLUMBUS & CRUISED UNEVENTFULLY UNTIL SOMETIME AFTER 1927 (AFTER THE PLT CONTACTED ARTCC & REPORTED MAINTAINING 9000'). STARTING AT 1953, ATTEMPTS TO CONTACT THE ACFT WERE UNSUCCESSFUL; BUT THE ACFT CONTINUED ON ITS ROUTE UNTIL 2018, THEN IT ENTERED A RGT DESCENDING TURN. RADAR CONTACT WAS LOST AT 2019 AFTER MORE VARIATIONS IN HDG & ALT. SUBSEQUENTLY, THE ACFT EXPERIENCED AN IN-FLT BREAKUP. AT THAT TIME, THE ACFT WAS BELIEVED TO HAVE BEEN APRX 188 LBS OVER ITS MAX WT LMT & 0.4 INCH BEHIND ITS AFT CG LMT. AN EXAM OF THE WRECKAGE SHOWED EVIDENCE OF POSITIVE OVERLOAD FAILURE OF THE WINGS & STABILATORS. THERE WAS EVIDENCETHAT THE ALTERNATOR LIGHT WAS ON, BUT THE ALTERNATOR, VOLTAGE REGULATOR & OVERVOLTAGE RELAY CHECKED GOOD. AT 2030, RADARDATA SHOWED PRECIP & CLD TOPS TO 14,000'. THE PLT HAD NOT MET THE IFR REQUIREMENTS OF 14 CFR 61.57.