... A "tainted" coin means one of the accounts in your transaction DAG was of questionable legality....
No, it doesn't mean that at all.
There are no coins. All Bitcoin is is a set of accounts and a series of transactions. You cannot taint something that does not exist.
... The only interesting question is: What happens if a court orders a "tainted" transaction rolled back?
The answer to your interesting question is that
nothing happens. You can't roll back a transaction without controlling the block chain.
You're assuming that the courts understand cryptos. They don't. Not until there's an expert witness testifies as to what they are. If a judge orders a rollback, he will expect it to be carried out without question.