If the calendar is associated with an email service like iCloud, Outlook.com, Yahoo, Google, AOL, etcetera, then more than likely the calendar events are still intact. Try the following:
1. Initiate the native Calendar app.
2. Select "Calendars" at the bottom of the screen.
3. Make sure there's a check mark next to your calendar(s). If no checkmate was visible and you've now placed a check mark next to the calendar by tapping on it, go to your calendar view to see if the event are once again visible.
4. If the above items do not work, logout of the associated email service, reboot your device and then reconfigure your device with that email service.