The max penalty for failing to file under FARA is 5 years and/or $10,000. Not sure he is conspiring against the US by engaging in lobbying efforts or introducing Ukrainian principals to law firms in the US. If the companies listed in the indictment owed US tax and did not pay, they should and will, but I could see any prison sentence on that running concurrent with the FARA registration fail. If he brought funds over illegally that may also bring jail time and payment of tax and penalties.
The other dude Papa-something plead really quick to lying to the FBI in July. He has probably been wearing a wire since about that time. But as with the Steele dossier, isn't it typical in politics to dig dirt on one's opponents? And btw, he never did get that dirt because the the Ukrainians / Russians would never give up their best pal madam secretary.
The relevant time periods do not seem like anything will stick to POTUS on these charges. And we're saying it's Russia collusion using the Ukraine as a proxy with deep cover agents? That's deep ... hip deep.