I believe you have to have procedures in place to revert back to paper statements
Not unless you've contracted for that means of handling bouncebacks. The e-Regs which used to require bounceback monitoring are gone. It's up to you and the customer. And don't forget--the whole idea behind e-delivery was to save money. You can't save anything if you're paying salaries to handle bouncebacks.
I've seen various ways of handling this problem, but the best is to set up two-tier pricing. Customers who elect paper statements pay a fee and customers who elect e-delivery don't pay a fee (or some variation on this pricing theme.) Included in the rules for free delivery is a condition, however, that the account automatically goes to paper delivery and the fees begin as soon as you experience a single bounceback. Customers would be able to request return to e-delivery and elimination of the fee if they provide a new EMA that checks out.