This is literally how embeds of everything on every service ever have always worked; don't pretend you haven't seen a grey box where a youtube video should have been. The only way for embeds not to work like this is A) use the definition of the embed itself to store the info, in which case it isn't an embed as much as it is a fancy hyperlink or B) do like twitter apparently was and not actually delete anything, which is stupid because then any tweet ever would be "undelete-able" simply by pretending you're displaying it as an embed. FWIW I'm pretty sure twitter has not ever worked as this article suggests as, again, that would be really stupid and I'm positive I've seen twitter embeds years ago which either don't load when the source is deleted or display some sort of 404 message like the site itself does.