There's no 'undelete' if that's what you're asking.
If you know the definition of the consraint, you can recreate it with ALTER TABLE. If not, restore the backup somewhere else, get the definition and recreate the default from that.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability
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