Start new process, without being a child of the spawning process

If the spawning process (parent) ends before the spawned process (child) does, then the parent-child chain is broken. To make use of this, you'd have to use an intermediate stub-process like so:

Caller.exe → Stub.exe → File.exe.

Here Stub.exe is simple launcher program that ends just after starting File.exe.

If you start a process, then you'll be its parent.

Maybe you could try to start your process from cmd.exe instead, so cmd.exe will be the parent.

Process proc = Process.Start(new ProcessStartInfo { Arguments = "/C explorer", FileName = "cmd", WindowStyle = ProcessWindowStyle.Hidden });