My advisor asked me to co-author a paper, but I have no interest in an academic career

Congratulations! In my opinion, it is perfectly polite to write back and say that you are interested, but can't afford to make a significant time commitment to the project. Ideally, the professor will be happy to do the work himself, and your role would largely be to look over the finished product, sign off on it, and make suggestions or comments.

It's fine to invite the professor to write this paper without you as a coauthor. That said, since you did much of the work already, the professor might prefer that you be listed as an author.

If you are thinking of possibly applying to graduate school in the future, it would probably be a good thing to have a publication under your belt.

Would there be anything to gain from doing this if I don't intend to pursue a career in academia?

Of course! You can put it in your CV. You might not need it for whatever job you're going for (are you sure you don't?), but you still have a rare opportunity that's worth bragging about which you give up by declining. Remember, the future is uncertain, and you cannot tell what you will need in the future.

For example here are some things which have come up unexpectedly for me:

• I once agreed to fill in for a friend for two weeks as a tutor. He wanted to switch to a full-time job but didn't want to leave his student hanging. I was not looking at a teaching career at the time, but four years later, I was able to cite this episode as teaching experience.
• I once put on my CV that I had some experience editing Wikipedia, which was relevant since I was applying for a publishing job. That later led to the company's marketing division asking me for help with navigating Wikipedia's conflict-of-interest policies (I was in the editorial department).
• And yes, I was in the same boat as you once: I graduated thinking I would never go for an advanced degree, but then changed my mind years later. I don't know how valuable the publication was, since my advisor wound up writing most of it, but it can't have had a negative impact.

Years from now, the time you spend to co-author this paper will look completely negligible. While it's possible there never are benefits, it's also possible that there will be, and that's when you want the paper under your belt.

This focuses on the first part of the question, i.e., whether there could be anything to gain from writing the paper. The other answers cover the second part.

Some industry jobs in computer science require or prefer applicants to have a master’s or PhD degree, or some research experience. If you wish to apply for such jobs now or in the future, a paper could help you to:

1. Strengthen your application or make you eligible for such jobs.
2. Strengthen your application for a graduate program if you decide to apply for one later, in order to become eligible for such jobs.
3. Maintain good relations with your professor in order to get a strong recommendation letter for applications in point 2.