That should not be the case. Yes, a hard reset will wipe all your contacts from the device, but it won't delete them from your computer. You should be able to delete the old activesync partnership and set up a new without losing any contacts. In any case,
PimBackup is your friend, it'll save all your contacts, etc. to a storage card and you can restore them after the reset. Or invest in something like
Sprite Backup or
Spb Backup. Both will allow you to completely restore your unit after a hard reset.