But even if the repaired wing had a problem it wouldn't have caused a loss of aircraft in such a manner (though it would have caused some difficulties to be sure).
What is most puzzling is the manner in which the aircraft disappeared. Not mayday call or anything. Even if the engines stopped turning there's batteries and ram air turbines to provide power for communications etc to get a call out.
So it's leading to speculation that the aircraft broke up at cruise altitude and other than acts of terrorism I don't think that's been an issue for many years.