How to convert free trial memberships to paid memberships

I currently have over 100 free trial members subscribed through the membership plugin and I now need to allow them to sign up for a paid subscription. Masonjames advised me to set the Trial membership as ‘finite’:

https://wpmudev.com/forums/topic/how-do-i-allow-free-trial-members-to-subscribe-to-paid-membership#post-76866

My question is, what happens to a member when they reach the ‘finite’ date? Are they deleted or are they simply deactivated? If they are simply deactivated they will not be able to use their current user name and e-mail to sign up for a paid membership as the sign up form does not allow that. How do I handle this to allow them to sign up for a paid membership with their old user name and e-mail?

I need to know exactly how to handle this or I am going to have over 100 angry women shouting at me.