2Nd Set of Formal Invites?

Our wedding is scheduled for August of this year. We are hopeful that we will still be able to have our wedding as we have planned but I have my back up dates already penciled in with all of our vendors. Thankfully, they have ALL been wonderful! In the event that I do have to cancel/postpone my wedding, I have the postponement cards all ready to go out. We will be postponing a year out. Is it necessary to resend a full blown formal invite at that time? Or can I ask our guests on our postponement card to go to our website and fill out a form that will give me an email address and send out a digital wedding invite the second time around?