the bottom line is once the game.exe can be loaded, it will be extracted to disk. You can't extract the bytes of game.exe and magically load that into memory as a process without putting it on disk first.

The very act of copying this exe to disk after extracting it from your exe, means the user could then simply copy the exe. It doesn't matter if you put it in some "obscure" place, it is very very simply to find out where a given exe is running from.

On that note as well, if you simply embedded the game.exe as an array of bytes into your main.exe as a resource, there are tools made specifically for simple extraction of resources from a .NET file.