He will not be deported. But he will be out of status and would be in his best interest to leave.
I agree the kid has the right to have a male figure in his life, but just because you got someone pregnant does not make you a father, merely a sperm donor.
As far as the whole, I want him deported thing... this could get messy if she acts this way (the divorce)... the more in agreement the couple are (about getting divorced) the easier (and cheaper) the divorce process will go.
But everything here has to do with agreements, contracts, two way commitments...
#1 "The both committed to love, honor and respect each other until death parts them"
#2 "She signed an Affidavit of Support, I-864, for him (and even if she divorces she would have to honor that if he becomes a resident for the next 10 years!)"
Her husband broke that first (and most important commitment, because regardless of whether she kept her part or not, it does not give you a right to cheat on her). Now... let's say they get divorced right after she lets him get the Green Card, then what?
He will pay child support? and she will pay "alien" alimonies or support to him as well?
She will be under a contract to actually support the guy because of the signed I-864 (Which only becomes legal binding if the residency is approved). But even if he pays child support for those two years, the guy still has to remove the conditions on the Green Card by himself (i-751) and I wonder how is he going to do that?
But if this is a "paper marriage", they will have a hard time proving a true marriage... maybe it was a mistake (getting married after 2 months)... but my true advice is... a cheating husband will cheat again, a cheating husband is not a good role model for a kid, and you will not benefit from the cheating husband getting a green card as you will be bound in a legal contract to support him for 10 years...
Like I said before, I would rather have a "happy" mom and perhaps a non-biological good dad... than a bitter mom and a cheating/lying father.