Switching payment gateways in Pro Sites?

What happens when I switch payment gateways in Pro Sites? I’m currently using Paypal Express, and have a number of subscriptions currently running. If I want to upgrade my Paypal account and start using Paypal Pro, what happens to the current subscriptions? Will switching to Pro break the existing integration, or will they play nice?

I’m a little gun-shy to make the switch since I can’t afford to have a payment glitch with my current subscribers!