A Vin Diesel helmed D&D film will very likely still miss the mark. Fantasy films are hard to pull off.
But getting him involved at least guarantees it will be a passion project for someone involved.
Matt Mercer has indicated on Twitter the session was indeed filmed and will be available to view.
https://mobile.twitter.com/matthewmercer/status/651193283268374529
This is Jeff Easley art from the days of 2nd edition, It was the cover of Eye of the Beholder and seems like it was named Trick or Treat.
Here is the artists website with the image
http://www.jeffeasleyart.com/See_Jeff_Easley_Art.html
While I am not sure if it was ever used in a d&d book...
I think it would be a mistake to make this a grim gritty serious fantasy movie. I would prefer it go "the gamers" route personally. Though I don't expect that.