The free 'JustDecompile app from Telerik can also create a new project from a .NET .exe file: [
^]. It's VS2015 ready and is being actively maintained, and developed, at this time.
However, if the programmer used obfuscation on the source, you are going to have more trouble than you already have.
The idea of the programmer "disappearing into thin air" seems a bit fanciful: unless you paid him, already, and there is a dispute about the deliverable, or about future work.