You will lose some data unless you reset the sync memory in DayLite.

We create a mapping between a DayLite Contact and an Address Book Contact. When you delete a record in the Address Book, we know that you did that because we have the mapping. We subsequently delete the DayLite Contact during the sync operation.

If you must delete your address book, please reset the sync memory in DayLite (in Preferences -> Address Book).

Note: You will have to launch Address Book once after the delete and before synching with DayLite.