The original authors might have a copyright claim, but it's not clear that Infocom (or its heirs) would.
If it was some sort of non-exclusive license, there should be no problem, because the authors seem to be on board with the release.
If the authors transferred their copyright to Infocom upon forming the company, then this code is technically no longer theirs to give away, especially since the IP rights were subsequently re-sold (maybe even multiple times).
I agree with others in this discussion that at this point, the code most likely has primarily academic/historical value. But that would not necessarily stop an owner from suing a deep pocketed entity like MIT.
But it's an interesting gray area certainly, as Zork was probably not "properly" prepared as a thesis/dissertation including MIT's recommended explicit statement granting the above non-exclusive license: "The author hereby grants to MIT permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part." [1]