"Set a single pricing model to charge for 36 months only."
It's a joke, to be honest, I don't think there should be a strategy, the only way to keep users is a "quality product" 1) providing value and 2) making them feel happy in using it.
but love to hear other opinions to open my mind...
In the simplest form, customer retention(https://www.corefactors.in/blog/...) is a metric to measure the percentage of customers you retained over some time and it helps you understand customer satisfaction with the product or service that you provided, their re-purchase behavior, and their bond with the brand.
The strategies for customer retention For SaaS are Define clear exceptions, offer connected upsell, create a communication schedule, etc.