Chosen Solution
I was unlucky to spill coffee on the keyboard. After drying it a bit the mac boots ok but retina display is very very dark. I can see that it works by using a flashlight and pointing it on apple logo at the back of the screen. I have attached external monitor via HDMI and all good. Apple service suggested to replace screen and motherboard total 1.6K :). Are there any other steps that I should follow to troubleshoot the problem and find the part to be replaced?
If you are good with your fingers and have the knowledge, you can replace the display yourself. The backlight of your display has burnt out, resulting in a picture but no light. You can follow the guide here, but getting your hands on a full display assembly might be a bit hard. EDIT: The guide listed actually has a link to purchase a new display assembly that is far cheaper than having it repaired by Apple, as only the display needs to be replaced. The part is used but is sold by Ifixit, so you can be confident that it has been fully tested and clean. Every part has a description of the condition of the item as well.
