Hi, MilSim. When paired with "SUCH", "AS" functions as a relative pronoun. In the sentence under discussion, "as" serves as the subject of the relative attributive clause. "Destroyed half the value of the bequest" is the predicate. As to the tense of the verb in the relative clause, it is contingent upon the context, not necessarily the simple past.
Thank you, f6pafd, for your reply. I realised precisely what you wrote about the verb not necessarily being in the simple past at a moment when I was unable to update my post, but I have now fixed it accordingly. Thank you!
I also realised somewhat late that this is another instance of the oft-discussed construction "as can be seen" (and its variations). There seem to be several "camps" when it comes to the role "as" plays (two interesting discussions can be found here and here). I appreciate your input and will search for a further treatment of the matter in my grammars (if you have any particular suggestions, please do share!)