What happens right now is this: ICE can run loose and do whatever they want. If some judge finds their activities illegal, they can block ICE from doing the illegal things.
But...who's going to stop them? Not the DOJ. Stephen Miller has said that ICE have "federal immunity". The keen observer will of course know that there's no such thing as "federal immunity", so a charitable way to interpret that statement is that no-one federal will go after them.
So what about states, and local police? Sure, they could start arresting them, but then again, Miller et. al have warned the states about not interfering, threatening with going after LEO's etc. with federal charges if they do so.
The long story made short is that they can (and will) keep doing illegal shit until someone stops them, and that's not going to happen as long as Trump is POTUS. DOJ and ICE leaderships has explicitly said that their workers should just ignore the law and courts.
Their budget right now is larger than the Marine Corps and a lot of their members are looking at unemployment or prison time if the democrats get back into control of the government. Think about what they are likely to do during the mid terms if they are told to monitor election sites. They are a gang of dangerously brutal violent thugs operating with complete impunity.
They're all going to receive a blanket pardon.
Well, we've already crossed into "the law is what I say it is" territory thanks to the republicans, so the next admin just needs to leverage that. The GOP thinks that pardons signed by autopen are invalid [0] so I don't see what would stop the democrats from apply the same logic to ICE agents and administration, except perhaps cowardice.
[0] https://thehill.com/homenews/house/5575379-house-gop-comer-d...
To the extent that their actions are unlawful, they are often crimes under state law in the states they occur, as well as federal law. The President of the United States has no power to pardon state law offenses (and while there may be political considerations that discourage pursuing charges while it might provoke conflict with the Trump Administration, but in many cases the statutes of limitations for violent crimes under state law are not short.