Why is my iPad dead/screen unresponsive after a week unused?

I have an iPad Air wifi model that has worked great since I purchased it. I’ve never had battery issues or dropped it, and typically run the battery down to 15-20% before recharging fully, though I have absentmindedly run it down a few times. A week ago it was working fine; after ~5 days of sitting it was unresponsive (black screen of death). The screen is just black and I cannot get it to respond no matter what I do.

I tried charging for hours via official cable and wall wart (no effect), hard reset (no effect) and even put it into DFU mode to attempt a restore (error 4005 after stalling at “Waiting for iPad” every time I try). I have tried multiple cables and USB ports, repaired my Apple Device Support install, and absolutely nothing works…I babied this iPad but it’s like it suddenly ceased working entirely just from sitting and I have no idea why. I almost wonder if an update bricked it. (Meanwhile my old iPad 2 which traveled the country with me at a former employer and has had a pretty rough life still works perfectly fine…)

At this point I have nothing to lose by taking it apart but need some suggestions on what to try when I’m in there first, unless there is anything else I’ve missed trying. What should I do?