What happens if 24 hour Platform Event limit is hit?

Platform event limits apply to a 24-hour cycle. Before delivering new events, such as a change in order status, to subscribed clients, Salesforce checks your allocation and how many events have been used in your Salesforce org in the last 24 hours. If the number of events used is lower than the 24-hour allocation, Salesforce delivers events to subscribers. If you did hit your allocation for events in the previous 24 hours, Salesforce doesn’t deliver new events. But, they’re queued within a brief time window until event allocation is available.

For other limitations in Platform Event - https://developer.salesforce.com/docs/atlas.en-us.212.0.platform_events.meta/platform_events/platform_event_limits.htm

Sample Platform Event Example - http://www.infallibletechie.com/2017/06/platform-events-in-salesforce.html