Great points. What gives me hope is that Trump proposes a strict Constitutionalist like those he originally posted. That will make up for Scalia. The next is to see which of the remaining Justices retires (or dies) before the case is heard. Some say that Thomas (also a conservative/originalist) may choose to retire if Scalia's replacement looks favorable. Ruth Bader Ginsburg is the top pick of the liberal Justices to retire given her age and that would surely be a huge blow to the Progressive cause, as she holds significantly more sway than any other liberal Justice currently.

I agree that Roberts is somewhat problematic along with Kennedy, because we can almost certainly count on Sotomayor, Kagan, and Breyer to vote for gun restrictions.

This assumes that the court will hear it. They almost certainly will but one is never sure about SCOTUS.
It also assumes that the justices will vote the way we think they will. Remember the Obamacare ruling.

The day that the 1934 National Firearms Act is declared completely unconstitutional again and this time by the Supreme Court will be a day for the greatest celebration since the end of the Revolutionary War.