What happens to memberships if you switch/drop a payment gateway?

What happens to subscriptions at renewal time if they signed up with a gateway that you have removed after they subscribed?

I currently accept Stripe, but would like to try adding others to see if I get a better conversion rate. If I don't, I'd like to go back to using Stripe only, but I don't know what will happened to the subscribers who signed up with the old gateway.

Any idea?