Matter of Andres Armendarez-Mendez, 24 I&N Dec. 646 (BIA 2008) (pursuant to 8 C.F.R. 1003.2(d) (2008), BIA lacks authority to reopen removal, deportation, or exclusion proceedings - whether on motion of noncitizen or sua sponte - if the noncitizen has departed the United States after those administrative proceedings have been completed).
http://www.usdoj.gov/eoir/vll/intdec/vol24/3626.pdf