Re: Did he jump or was he pushed?
"So it would appear that things were sabotaged to create unbearable working conditions for the new IT director."
How so? I see nothing in the original post that indicated sabotage. What I see indicates an age-old story - he turned up with his own ideas, and didn't bother to due appropriate due diligence before implementing them.
It seems fairly obvious that the company had a very customised workflow in Notes, and in my experience any project moving away from that will be a multi-year endeavour. Most companies start the migration with mail, then move on to applications. Mail migration usually takes a year or two just by itself, and after that you need to run coexistence tools so that the email from workflow applications still gets delivered properly, so it's expensive.
Maybe he'd previously done this quickly in a smaller organisation that had less customisation? Maybe he just didn't know or care about the challenges, and was being brought in by the rest of the management to be the fall guy?
"He was being set up to fail."
By himself. Not by anyone else, except possibly the management as mentioned above. A new IT Director arriving with grand plans that fail is a story as old as time. Just because you don't like the product being replaced, that doesn't mean you should assume that the failure was anything more unusual than the other ones we end up talking about here.
"In 2024 it would seem that his assessment to gradually retire Notes was the correct one"
I don't disagree with the first part of that sentence, but would like to take you up on the second one. The OP did not talk about a gradual retirement. They spoke about a two year deadline to remove Notes. Nothing gradual about that, which is why I said above that he set himself up to fail. No sabotage from anyone else required, he brought all that he needed with him.
Two years is, as I've mentioned above, just too short. Based upon the workflows described I'd guess that they had fairly heavy automation of business processes in Notes. At a rough guess they probably had an application that created their contracts as multiple documents in a Notes database, possibly pulling item specifications out from a separate document store (also a Notes database) and then just automated the printing of it with a button on the view. It probably also had some light review features for routing through management and legal to ensure everything was OK. Nothing difficult for Notes, and possible in SharePoint, but not as easy.
So I'd guess that removing Notes in this organisation would be a six to ten year project, not two. That's based on an estimate of at least 500-1000 seats, and I'm having to guess that based on the size of contracts being mentioned, so it's not a precise figure.
You're going to have a year of requirements gathering and usage auditing - identifying what's used and what it can be replaced by. You then should start a two year mail migration, alongside prototyping for the new applications on their respective platforms. Then once mail is completed you ramp up the application migrations. It will be very expensive, as you're going to need to employ a number of contractors or employ development services, not to mention the possibility of temporary staff to help with the logistics of the mail migration.
Want to take a friendly bet that the IT Director underestimated costs and did it on the cheap? ;-)
I'd like to make a final note about the OP's comments on Word and long documents. Basically, that rings true. Microsoft disabled the "fast save" by default feature in 2007, and that was notorious for losing data especially in longer or more complex documents. Word has gotten better in more recent versions, probably because of work done to enable incremental saving to the cloud and collaborative working, but I still find myself nervous at work if the document gets long. (And at home I use different tools anyway, so it's not an issue.)