It may be possible for us to track down the date/time person that deleted the Defect Suite if it has been deleted fairly recently. But if a Defect Suite is deleted, there is no way to restore it as Defect Suites are not supported by the Recycle Bin.
On a good note, deleting the Defect Suite does not delete the defects. Only the association between the defect suite and the defects are removed. You will be able to recreate the Defect Suite and re-associate the defects.
Please open a case with us if you would like us to try to determine date/user that deleted the Defect Suite.
You can use our lookback API to find the defects that were attached to the Defect Suite here: https://ca-broadcom.wolkenservicedesk.com/external/article?articleId=212438