christopher flowers , 84 , was driving on rochester , ny , street on march 9 .
dropped lit cigarette , causing several layers of clothes to burst into flames .
three drivers stopped to help as fire engulfed pensioner 's torso and head .
one tried to put out flames with hands ; another threw him into snow bank .
flowers , from chili , rushed to strong memorial hospital with severe burns .
on sunday , hospitals officials announced retired marine has passed away .