I'm going to start by saying I haven't read all 3 pages of posts. I just found this thread.
But this is what I think will happen.
After researching and reading all the articles on defensive gun uses (DGUs) in MA, I'm pretty confident that if you assume it's 100% clean, there won't be any arrest.
I think there is also a reasonable chance that your LTC will be pulled while they investigate. Which means that in the time after a DGU you need to get your firearms out of your possession. Without charges you won't be a federally prohibited person, so simply driving them over state lines into a free state should suffice.
But if you don't have a friend in another state, then bring them to your local dealer and have them book them in.
Of note, is that if you have AR type firearms you should remove the uppers, since they aren't firearms and give them to a friend to hold.
If the cops come, they will take all of your scopes, gun parts, etc, even though the law doesn't authorize that. Bring them to a friends also.
If you want to press things, you could make the argument that a stripped frame, while a firearm per fed law, is not a firearm per MA law and is therefore not subject to any MA firearms laws. So if you strip everything down and hand the lowers and frames to a local gun hating friend who does not have a LTC, then you will be safe. Note that MA safe storage laws don't apply to stripped lowers/frames. So the friend would not have to own a safe.
I wouldn't do that, but it's legally sound. IMHO, the best thing to do is simply move them out of state. It's not logistically complex, expensive or time consuming and is 100% legal.
Then, if nothing happens and your town does not pull your LTC, it's easy and free to get them back.