If a respondent has obtained post-conviction relief in the court of conviction, respondent can ask the immigration judge or Board of Immigration Appeals sua sponte to reopen removal proceedings based upon a gross miscarriage of justice. There is a line of cases in the Ninth Circuit (Cardoso-Tlaseca v. Gonzalez, 460 F.3d 1103 (9th Cir. 2006); Estrada-Rosales v. INS, 645 F.2d 819 (9th Cir. 1981); Wiedersperg v. INS, 896 F.2d 1179 (9th Cir. 1990)) that supports the argument that if the prior conviction was vacated on constitutional grounds, the removal was illegal and ought not to stand. Where the prior conviction was later found by the Ninth Circuit in a criminal proceeding not to have supported the ground of removal, the immigration courts could follow the same procedure, but the argument will be different. The argument would be stronger if the IJ was wrong from the beginning about the law, as opposed to a situation in which the law has evolved since the original removal order and is now favorable.
Thanks to Maria Andrade.