Long answer: Most nurture programs have a natural end date. Typically, that end date is defined by the end of a string of emails written and deployed in a marketing system (automated or otherwise).
This end date, of course, is usually arbitrary and ridiculous. How do you really know when a prospect is dead and gone forever? How do you know how long they’ll actually take to mature into a qualified and ready-to-buy prospect?
Another key to how you answer this question is the quality of the content you’re using to nurture. If you’re pushing content about yourself – your products, their features, use cases, etc. – the end of a nurture campaign is likely more defined by when the prospect gets sick of your thinly-veiled sales pitches.
However, on the other hand, if your nurture program is about the customer – addressing their needs, educating them on things that help them throughout their business, making them more successful even if they’re not handing over money (now or ever) – then the nurture may never end.
You may nurture a prospect for years before they convert. That’s a long time, but I assume you still want that business when the prospect is ready to move. You may also nurture a prospect for years who never converts, but who sends you referrals from others they know are closer to needing your solution.
The incremental cost of sending another email is minimal. The incremental cost of one more person reading your content is zero. So why would you intentionally cut off communication with someone who could directly or indirectly help your business, be it tomorrow or five years from now?