I think you are overestimating a bit: killing the government employees would reduce GDP. The government may not directly produce GDP, but it is essential for providing the conditions for business. Simply cutting away the peaceful enforcement of contracts and peaceful settlement of disputes privided by the government (two major purposes of the courts and police) would have immediate negative consequences. Within a few years you would also feel the consequences of nobody planning, building and maintaining infrastructure, or collecting the taxes to do so.