I deleted all events in Google Calendar thought I didn't need them anymore some day, but I regret it now, fortunately I have all of them in the Google Calendar app of my phone (Android Jellybean), my phone is not synced with my Google account at this time, the problem is how do I sync them back? I'm worried about losing the events in my phone too if I enable sync.
Download iCal Import Export 2.2 from the play store and you can backup the calendar on your phone. Move the file to your pc and follow the instructions here: https://support.google.com/calendar/answer/37118?hl=en to upload to your Google calendar online.
Or maybe you can just turn sync on? That I don't know. But create the backup first if you try it!