Your IT guys need to restore it from their most recent backup.
I personally do not own a blackberry but have worked with the Blackberry BES admin involving the devices. If I am not mistaken, when you synch your device there is a setting to set either the device or the outlook calendar as the primary calendar. If the blackberry is the primary, you need to switch it so the outlook calendar is primary. Sync the blackberry calendar back to the outlook calendar first. Another thing to check is if you are auto-archiving your calendar. If you are, then the previous entries will be moved off your “live” calendar to your archive calendar. Open your archive file in outlook and check the calendar there and see if your entries are there.
Do you mean that all apointments are gone form exhange? If so, a restore is needed. If Exhcnage holds still appointments, you have to find the hidden feature in blackberry. There is a combination of keys that completely rebuild the calendar without the need to wipe and reactivate the blackberry .