Your event page groups everyone who has not answered, with the count on the header and one action beside it: nudge them.
The message is written for you and you can edit it before it goes. It names you, says which event, and asks for a yes or a no. It goes to each person individually — nobody sees who else is on the list.
We also send one nudge automatically, three days after the invite went out, or a day after if the event is less than five days away. If you would rather do it yourself, turn reminders off in the event's options.
Two limits exist, both on purpose: nobody gets nudged twice within 48 hours, and nobody gets more than a couple of nudges in total. Someone who is not answering has already told you something.
Anyone who has replied anything at all is left out of a nudge, including people who said not sure yet — they get their own check-back on the day they were promised one.