You have a contract, and you fulfil your side of it when you deliver the work. The NUJ recommends that any work commissioned and delivered on time and to specification should be paid for in full, whatever happens to it after that.
Editors who have over-commissioned, changed their minds, or (especially) taken over a previous commissioning editor's job often offer a "kill fee", typically half the agreed fee, instead of the full amount.
The freelance still has to decide whether to press the issue.
If it seems that an editor may be unprofessional enough to find personal animosity in this simple contractual matter, the freelance has to make a judgement on whether they want to work again for such a client.
As always: Negotiate!. As always: to negotiate calmly and reasonably is a sign of professionalism, not of awkwardness.
How much time you put into this may depend, however, on whether the article is time-limited and what other outlets exist. It may be worth reminding the editor that, while Marks and Spencer are famed for a flexible policy on customers returning goods which they bought but later changed their mind about, they don't take sandwiches back and they don't take underwear back.
The National Union of Journalists must not, can not and would not wish to dictate rates or terms of engagement to members or to editors. The information presented here is for guidance and as an aid to equitable negotiation only.
Suggestions apply to contracts governed by UK law only. In any event, nothing here should be construed as legal advice.