As a bit of background I work on a C# WPF .Net 4.0 application which is deployed to several hundred machines running POSReady 2009. POSReady 2009 is still in support until April 2019 but the highest framework version it supports is 4.0 which will be out of support on 12/01/2016.
I very rarely contact Microsoft for technical support (and they haven't been particularly helpful when I have). This machines tend to be on private networks and are not accessible from the internet.
What are the disadvantages of continuing to use .Net 4.0 after the end of support date?