If you own the product, you own the product. Even with the new subscription model in place, you can opt buy the product as you did before and not pay a subscription.
The subscription is a leasing option. If you don't have the $$ to buy it you can lease it for a period of time. Existing customers can join the subscription program for free updates to any products or can continue using the software they own.
The short answer is that it won't effect you at all unless you decide you want to be part of the program. If you do join and you have previously purchased, then if you cancel the subscription you can continue using the software you purchased. People who have not purchased and cancel the subscription will no longer be able to use the tools, but all web sites created will continue to function normally.
There is really nothing for existing custmers to be afraid of, we are just trying to lower the barrier to entry for new customers and offer a subscription model for those who want to be ensured the latest version of everything at a fixed annual cost.