Presumably Blue Team are all employees of some company ("the employer"), so the software is a work for hire and copyright is owned by the employer.
However in the UK and some other countries (but not in the US) authors also have "moral rights" over their work, including attribution, integrity, and association of an author to the work.
This article (by Canadian lawyer Mark H. Evans) discusses the question of moral rights in works for hire:
For example, if a former employee wrote a blog to promote a company’s services that was published on the company’s website under that author’s name, the company might find itself being sued for breach of the author’s moral rights if it were to delete the author’s name and replace it with the name of an employee who wasn’t the author but is still with the company.
On the face of it John would be in a similar position to the blog author in the quote. So for the employer (including Jane, as an employee) to remove John's name would be a violation of his moral rights to attribution.
In this case the source code is public. However in most commercial settings it would be secret:
The secrecy of the code would make it harder for John to find out his name had been removed. However lets suppose that a friend still in Blue Team were to tell him. I'm not sure about discovery rules in various countries, but presumably a serious lawsuit could get confirmation.
The secrecy of the source code also means that fewer people would see John's name there than if it were generally published. This would lessen the damages, but not eliminate them. John would probably be able to get an injunction ordering that his name be restored.
Many programs are published with a credit list, and John would certainly have a moral right to appear on such a list with the same prominence as other team members.
From later in the same article:
While moral rights are personal and can’t be assigned, they can be waived. This is an important solution to navigating moral rights in works generated by employees and contractors. And because any assignment of copyright is not an automatic waiver of moral rights, the waiver must be express.
So it depends on the contract between John and the employer. If John has explicitly waived his right to attribution then the employer is in the clear.