We walk-up to restaurants all the time with the knowledge we may be turned away and will need to eat elsewhere. Sometimes we've gotten lucky and sometimes we haven't. No one here will be able to tell you if you will be able to get a walk-up or not. If you really want to eat there, make the ADR. If you can handle being turned away and eating somewhere else, go for it! The good news for EP is, if you do get turned away, there are some great QS restaurants there! (but apparently not the Via Napoli pizza window, LOL!)