America's govt didn't change their mind they're taking him to court because they say he's guilty. If it's easy like you say he'll be freed but if the case's strong against him he's going to have difficult days with the judge & jury. The case against Tornado Cash's dropped so they should drop it against Roman Storm.
I don't expect him to be held solely responsible now that the case against the project itself has been dropped. Prosecutors will seek to charge him with facilitating money laundering and may even attempt to prove his involvement in financing terrorist activities, but I believe it will not be difficult for his lawyer team to drop those charges based on the dismissal of the main case and the fact that no transfer related to suspicious activities can be proven. Ultimately, they will sentence him to pay a fine and pledge not to engage in similar practices. The service code is automated and cannot be stopped or modified, so any sentences against Roman are meaningless.