// if it isn't against any specific law, he has no need to act on this decision //
Depends on what the Court says. For example the Scottish Court ruled that it was unlawful but then also decided not to enforce that ruling, pending the Supreme Court ruling. If the SC agrees with the Scottish Court, and also ruled that the government *must* reverse that decision, then it would be obliged to listen. And besides, Johnson has already undercut that: he has already said that if the Supreme Court ruled against him then he'd recall Parliament.