Flight Instructor reported a pilot knowingly departed from a non-towered airport opposite direction to the reporter who was on final approach resulting in a NMAC.

Narrative

[I am a] CFI with the FBO at ZZZ. This afternoon you took off with Aircraft Y from ZZZ on runway XXL and after departure you were maintaining 270 course. You knew that at the same time there was an IFR aircraft shooting the ILS XYR approach at ZZZ; in fact it was myself in Aircraft X. You have been previously informed about that by ZZZ delivery before your takeoff; nevertheless you decided to depart in VFR and to continue on your 270 course. Your decision put both airplanes in a very close mid air collision. That happened at 1;600ft. While still in contact with the ATC; I was maintaining the altitude to reach ZZZZZ; which is the FAF on the ILS procedure; ready to intercept the glide slope. The cloud visibility at that altitude was much less than 1/2 mile; in deep IMC (ceiling about 700 ft). The ATC was busy to talk to other traffics and it did not have the time to alert me. So when I noticed the inevitable collision I had to briskly veer to the right and rapidly descend by 500 ft. Only after this avoidance maneuver I called the ATC that told me if I was able to climb again and rejoin the localizer; which I did. I am here to tell you that what you did today was not only very unsafe but also it could have lead to a very tragic event. You took off in VMC and you were not authorized for any reason to fly in the clouds in IMC; in addition knowing that there was an IFR traffic on the opposite course. I will file a report and I will inform by letter ZZZ ATC. I hope that in the future you will not behave like that; putting again other people's lives in serious danger......any other comment is superfluous.