No they wouldn't honour the mailers for Kodachrome, all film had to be with Kodak Lausanne in Switzerland by the 31st of October 2010 as that was the date of the last shipment that they made to Dwaynes in Kansas for the processing. Dwaynes did still continue processing though until the 31st of December 2010 officially although they ended up with such as backlog of last minute rolls sent in that they didn't finish until mid January 2011 (and had to place an emergency order for the chemicals with Kodak as they had underestimated how much they would get!).
Keep any rolls of undeveloped Kodachrome, there are several efforts ongoing at various labs and groups to resurect the processing to develop rolls like yours in colour (B&W neg processing is fairly easy with Kodachrome as it is a B&W film anyway with the colour dyes added in during development).