[SERIOUS] Question about how to manage churn?

I am looking for a good way to manage my churned customers. I am in a SaaS company that sells to other businesses in the HR industry. Our sales cycle can be anywhere from 30-days to 90-days before a close (sometimes more). Of course, we want to win back our churned customers but we also don't want to just delete them from our CRM. What do some other folks do? Do you put them into a kind of limbo for a period and then kick them back to leads (or earlier). How do you look at lost customers and their potential for win-back?