There's this thing people can buy called 'Extended Support' from Microsoft and you will continue to get security patches for their legacy OS's. If your company can't shell out a few bucks for this I don't see how it is Microsoft's fault. I'm sure there is other software in your environment that has similar support contracts why is Microsoft singled out? 10 years is a long time to support a product.
If you've got another job lined up and they want you in three weeks your hands may be tied but if the new place can give you some leeway or if the old place doesn't mind paying you whatever figure you give them per hour you may be able to help them out after you leave.