Macbook Pro on but display is blank

Was using the MacBook Pro a few days ago without any issues. Shut the lid in the middle of working, went to a coffee shop, and upon opening it back up the display was blank even though the computer was on. All typical manner of restarting it, recovery mode, power in, etc. changed nothing. External monitor in the HDMI port, also nothing.

Eventually, I realized that the display was on but extremely faint (could barely make out some lines). I was able to log in, close the alert box that said my Mac had turned off unexpectedly, and launched the terminal. After that day I've never been able to make anything out of the display since.

I was able to turn on remote screen sharing via the terminal and connect via my other computer over the network. This let me do some further troubleshooting.

• Plugging in an external monitor via HDMI, or ThunderBolt2->HDMI adapter and then HDMI do nothing, do not register another display or in the System Report it says nothing is plugged into the Thunderbolt port
• The display was listed as "Built-in Display, 23-inch, 1280x1024, Intel HD Graphics 4000" in About this Mac. In the display menu in the top right it refers to it as "Connected Projector: Built-In Display". In System Report it's "1280 x 1024 (SXGA - Super eXtended Graphics Array)" and listed as Main Display: Yes
• After swapping out HDMI cables into a couple different monitors and different ports to cover all use cases, it eventually referred to the display correctly, as a 15.4" Retina Display. It still didn't work, though, and after rebooting it went back to the erroneous label.
• Casting the display over Air Play does work
• The only issue I noticed prior to this is the fan was a little "choppy" (it would still get louder/quieter as normal with more work... but it sounded choppy like it was dirty though compressed air didn't resolve it).

Does this point to any issue in particular? I've had the display fail on an old MacBook in the past, but an external display didn't have any problems. I've been quoted a logic board replacement but I'm worried about spending ~$800 on a laptop that might be worth ~$1200 new and then run into other problems in the future.

I realized that the display was on but extremely faint (could barely make out some lines).

It’s your video mux and your back light.

This is a telltale symptom that your back light is out. However, you have additional symptoms, that compound this problem.

The LED back light is exactly what it sounds like - it's the light behind the LCD that makes what’s on it visible. It could be the light itself, the fuse, or any of the electronic circuity that handles it.

Now, the video mux (multiplexer) is a chip that handles the “switching” of the video signal between the internal and external displays and where applicable the integrated and discrete video adapters.

This may be a coincidence or it could be some common components that have failed. Either way, this is not a DIY fix - it’s something you’ll have to take it in for service.