Burt is told near the beginning of the episode that if his mother-in-law were to die before the end of the year he wouldn't owe any estate taxes. While it is true that the estate tax was repealed in 2010 and therefore would have no affect, in 2009 estate taxes were only due on estates totaling more than $3.5 million and in 2011 for those totaling over $5.0 million. It is highly unlikely that Maw-Maw's estate would reach these amounts so no tax would be due regardless.