Publication in a journal that has now disappeared entirely. Can I publish the paper elsewhere?

I published a paper with some co-authors in a national journal, recently launched, that was promising at the time. It got accepted after a few rounds (yay!). Unfortunately, for some reason, the journal was discontinued a few years later. Now the paper is not accessible as the journal does not have a website anymore. There are some traces of the paper online (it got cited) but this is all. No one can read it anymore.

Am I ethically allowed to submit the paper elsewhere for publication? It is a bit of a weird situation: the paper was published, but it is not published or accessible anymore ...

You paper is still, in principle, accessible through some libraries, e.g. the US Library of Congress (but you should check). Even for fully electronic journals, libraries use the LOCKSS system to archive papers published there: https://www.lockss.org.

Your paper still counts as a publication for the purposes of academic advancements. Regardless who holds the copyright, publishing it again (likely) would not be looked at kindly by the academic institution where you are in, and I recommend against doing this. (You also will get into trouble with another journal where you would attempt to publish your paper since their copyright agreement would typically contain a sentence similar to "...the work has not been published before, in any form, except as a preprint.")

Some publishers allow you to post a prepublication version of a published paper on arXiv, or bioRxiv or on a personal website, even if you do not hold copyright. (But you would have to check with the publisher first.) If they allow this, this would be my suggestion.

There is one more option: If you are planning to write a book on the subject related to your paper, you can include material based on your paper (but don't copy it verbatim).

A few additional thoughts, none of which requires re-submitting the paper:

As Buffy says, the relevant license is usually granted to the publisher, who may still exist. In that case, contact them and ask. If they allow you to make a copy of the original article available, go ahead and do so (this does not even require "getting back" the copyright, it can be done via a further license that does not require them to give up all the rights you granted them).

What you can always do is to publish the information how people can contact you about this paper whose journal ceased to exist, e.g. on your professional/university web page, or using services like researchgate, academia.edu or the like.

It's certainly also worth while to check the license agreement with the journal: you may anyways have retained a right to publish a manuscript version of the paper, e.g. on arXiv or the like. (see also below)

Copyright in your legislation may offer several possibilities. E.g. if you were in germany:

(1) Where the author permits the inclusion of the work in a collection which is published periodically, then, in cases of doubt, the publisher or editor acquires an exclusive right of reproduction, distribution and making available to the public. However, the author may otherwise reproduce, distribute and make available to the public the work upon expiry of one year, unless otherwise agreed.

[...]

(4) The author of a scientific contribution which results from research activities at least half of which were financed by public funds and which was reprinted in a collection which is published periodically at least twice per year also has the right, if he or she has granted the publisher or editor an exclusive right of use, to make the contribution available to the public upon expiry of 12 months after first publication in the accepted manuscript version, unless this serves a commercial purpose. The source of the first publication must be cited. Any deviating agreement to the detriment of the author is ineffective.

(1) Up to 15 per cent of a work may be reproduced, distributed and made available to the public for the purpose of non-commercial scientific research

for a specifically delimited circle of persons for their personal scientific research and

for individual third persons insofar as this serves the monitoring of the quality of scientific research.

[...]

(3) In derogation from subsections (1) and (2), full use may be made of illustrations, individual articles from the same professional or scientific journal, other small-scale works and out-of-commerce works.

German copyright law also knows the special status of an orphaned work whose copyright holder cannot be found (§61 ff UrhG) - in case the publisher of the journal ceased to exist and the license was not transferred to anyone else.

In that case, I'd recommend talking to your library - they should know what can be done.

You can't publish something for which you don't hold copyright. In the past one almost always gave up copyright to the publisher. Today, in some systems, it might be only a perpetual but non-exclusive license that you give them. Back then, authors were given back a license for some uses, but probably not the right to republish. You were given some documents when you turned over copyright or a license. Try to find those so that you know what rights you retain.

If you don't have copyright or a very broad license, then you can try to contact the publisher of the original journal (or any successor) and attempt to get back your copyright. They might be fine with it if they have no further economic interest in the paper. But it is up to them.

Note that the publisher may still exist even if the journal does not. And if the publisher has gone out of business they may have passed all assets to a successor company. Those assets would include any copyrights they hold. You might need to do some research or hire an IP lawyer to work it out.

You are asking the wrong question. You should not think about publishing the paper a second time (including review, claiming novelty etc.), but making the paper ease to find and access for interested readers.

The easiest way is uploading it to arXiv and you personal website. I would not be concered regarding copyright issues, as the journal is discontinued probably nobody is going to complain.

Maybe you can increase visibility with a link from ReasearchGate and your Google Scholar page.