In the version 8 beta, there is an undo feature that is visible for a few seconds:
but after that unfortunately it will be lost as there is no trash folder for events. But you may be able to restore them from your most recent backup.
Because restoring the backup may delete any new data, you will first need to make a new backup (call it backup1), then disconnect from the Intenet and restore the previous backup. Find the items you deleted and export them (Save As). Restore backup1 so you are back to where you were a few minutes back, reconnect to the Internet, and then import the items you lost.