Yes, cross-posts should be deleted.
They should not have been posted in the first place, and thus their proper state of existence is none at all.
Note that it was a diamond moderator, acting in that capacity, who deleted your question. Here is his comment regarding that action¹ (bold emphasis mine):
Thank you for being persistent, but avoid reposting or cross-posting to get more attention. See: “How do I get attention for one of my own questions without a good answer? – Meta Stack Exchange” If you want to try another site, ask for migration, or else delete the original before re-asking the question on the other site. See: “Is cross-posting a question on multiple Stack Exchange sites permitted if the question is on-topic for each site? – Meta Stack Exchange”. – MetaEd♦︎︎ 8 hours ago
You don’t need more affirmation than that as to the disposition of this site towards that action.
Please do not cross-post; if you choose to ignore that injunction, than you should not be surprised or cavil at the obvious consequences.
We — specifically you and I, you asking, me answering — have discussed this before, on this very site. In the selfsame question you are asking about, I brought that discussion back to your attention. We do not need to discuss it again.
That policy outlined here, on Meta.EL&U, is more pertinent and binding on EL&U than any other statements, pro, contra, or otherwise, that you find on MSE or any other meta site you care to reference².
¹For users < 10k who cannot see it; I’m aware that as OP you can see your own deleted question, and have already read it.
² And if you insist on doing so, you should use the normative link the moderator who deleted your question provided to you in the comment he left when doing so. The very same link I provided to you four years ago when we discussed this the first time. The topmost and accepted answer is “no”, where both the question and the answer has more votes, thus more consensus, thus more weight, than the two contra posts you cite. The answer is no. You’re going to have to accept that.
No, I don't think questions should be deleted just because they were cross-posted.
If non-mod users can migrate questions between the two sites, then vote to migrate one of them, and make a note to members of the other site to close it as a duplicate of the purported cross-post.
For example, suppose "X" on EL&U was cross-posted as "Y" on ELL:
- migrate "X" to ELL
- leaving a comment on "X" to ask ELL members to close "X" as duplicate of "Y".
There's the theoretical possibility that both will be migrated both ways, but I don't think it would happen all that often.
Otherwise (i.e. if non-mod users can't migrate questions between the two sites), the question ought to attract different kinds of answers on both sites (e.g. EL&U and Physics), so it should be treated independently on each site. Each site can deal with its own question independently: keep open, close, dupe, delete, etc.