Maybe. But these are all hypotheticals. The article presents it as I should be morally disgusted by this move. I don't really see it.
I agree that this closure is not world-ending, and I think the point of the article is that if MS can do this to your ebooks, then other big tech companies could do it to your other content too.
Personally, while I might not expend the effort on some random novel (though I do highlight quotes I find particularly insightful or funny), I do make a lot of in-line notes & highlights on non-fiction books, both paper and digital. I'd be really pissed off if a book I studied disappeared with all annotations. That's why I learned to procure PDFs of e-books I care about, and I recently started to maintain a separate folder with "reading notes", into which I retype my annotations and thoughts on them after I'm done with reading (this means essentially re-reading the book, albeit much faster, as I have annotations to guide me to important thoughts).
The vendor is providing a full refund to customers including an additional $25 credit for customers who used the annotation service.
DRM is an annoying customer unfriendly solution to a problem that I'm not convinced exists... but people have been given full access to these books for a while. They've been able to read them from date of purchase until now. Some of them are probably finished reading the books and I'm sure "more than a few people" have exported their books to open formats.
Microsoft has handled this as gracefully as it could, all things told.