At worst, he could potentially be barred from becoming a citizen of the U.S. Typically, an illegal alien cannot become a U.S. Citizen without going through the proper channels. Fortunately, for your husband there is an exception for aliens who arrive in the country legally and then overstay their visa due to marriage. This sounds like your husband's situation. And should he leave the U.S. he wouldn't be barred from becoming a U.S. citizen at some point in the future. At worst, he might be subject to an 8-10 year ban for his conduct though.