Hello there! I'm a bit confused as to why you would need the microphone track on another file, rather than in the same file but in another track; it probably does what you want it to do. Let me explain.
You want game audio and microphone audio to be separated, correct? In that case, you can open the "Mixer" thing in the "homescreen" of OBS, there you can set each and every device of yours to a particular track, numbered one to four. Just tick one device per track (EG: game sound to track one, microphone to track two, leaving everything else unchecked). When you open a video with these settings on a video editor, you will have x number of audio tracks, depending on how many different audio sources you have, all separated, one per track. It simplifies audio cutting and stuff. I hope you find this useful! Screencap to make things easier.
