If they ban LC subs, I140 which are being processed and used sibstituted LC will be rejected, immediately, in case if decesion is not made regarding those I140. I do not know about I485.
I don't think anything like that would happen. If the new law is placed it would be for new applications and will not apply for pending applications. That is how laws are usually implemented. Or else USCIS will have to face a slew of lawsuits and USCIS's action would most probably not hold up in a court of law.