Churn prevention measures can be applied to recurrent and pre-paid/one-time businesses. But how you measure churn plays an important role.

In your case, assuming no product usage for 3 months as a churn indicator is not serving you well, you need to figure out the average number of days/weeks your product was used for the already churned customers. You can use that as a good churn measure(without any assumptions).

But to pinpoint potential churn exactly and implement retention actions, you need to use more data points on your customers.
– Segmentation/Tiering of your customers
– Customer Demographics(Industry, Emp, Rev)
– Core product feature Usage(Breadth & Depth)
– NPS/CSAT surveys
– Sentiment