I can't see a settlement costing existing users any additional money. We don't pay money to RIM, we pay it to our carrier. The reason we pay more is that because for each device that the carrier provisions right now, the carrier pays RIM a portion of money.
If there is a 'shutdown', RIM will not be allowed to provide the service to the carriers, which should in fact cause a reduction in what existing users pay, due to the fact that the carrier now doesn't have to shell money to RIM each month for the number of handhelds on the network using the blackberry APN.
To make it real simple, the shutdown means that the blackberry APN will end up becoming a sup'd up regular APN, and that our browsing might have to go through that... but then again, I live in Canada and won't have that issue.