I don't know about *missing* per se, but it's a classic case of a 50s modern-but-not-really urban background building. And it's good-mannered, cheesy blue spandrels and all--it certainly melds right into the Bay St fray.
On that level, at least, it's a sorta-loss--or at least, something which merits deeper appreciation and understanding than a simple red-X-and-leave-it-at-that.
Note: that's not so much a "heritage" argument, as a "comprehensive urban survey" argument. (And I remembering offering it in the past re the now-gone Goodwill complex...)