[BScout]

If you previously had a working HDX system (and it seems you did with 12.4 and HD software), you are grandfathered in and will be given a free Digilink license.
If you do a reinstatement and it isn't auto-included with the upgrade (but it should be part of a perpetual bundle for upgrades which would include a bundle license of: 10 HD,11 HD,12 HD, 2018HD , Digilink licenses), then contact support and they'll send you the license. This is different for new HD users who won't get a bundle but only the latest. And if you didn't have the hardware prior to a certain date, then the Digilink license would need to be bought too. But if you had 12.4, you were before that cut off date.

As for jumping ship, I fully believe in seeing the other side of the fence. I still see Pro Tools MIDI as being 5 steps (or more) behind the big guys (Logic and Cubendo) but for mixing/routing, I think Pro Tools is still the best.

If you are moving more to scoring, you might prefer the MIDI features in the others. I wouldn't sell your Pro Tools gear though even if you freeze where you are at -- you still need compatibility with the Film/TV world if you intend to really "make it". Here, I'm talking actually scoring to picture (vs doing library tracks) where you'll work with edit rooms and music editors.