Escaping the Digital Dark Age

>MIT AI...

Not all, ITS and PDP10 can be emulated under Simh classic. Or you clone their github repo

       https://github.com/PDP-10/its

and run

       make download EMULATOR=pdp10-ka

Macsyma, Lisp, Emacs, Adventure... are still alive. And maybe tons of code lying in the disk image.

On truly lost stuff, I'd say the LSD-1 under the PDP10, which was a proto-vr/FPS walking around a wireframed town:

https://www.sfmoma.org/artwork/2015.9.12/

More info:

https://github.com/PDP-10/its/issues/616

Yes, you can recreate it in a weekend with SDL2/C and basic trigonometry, but the original it's lost.