Dave I reckon most should be salvageable as the ones I have had so far have been on the probing and hence are uncut sections. Also starting again is often not an option, expensive material, lack of more material etc.
When I was doing the round flange in stainless the last day it failed after the first hole, then after the third then I think it cut the last 3 circles but maybe it failed once more, can't quite recall. Anyway I only had one piece of 5mm stainless big enough so I had to make it work and with RFH not working I had to edit the code to miss out the holes already cut, PITA but it worked.
Yesterday I was doing quite a large file, a 400mm x 400mm Santa Claus head in 4mm Alu, halfway through the code called for it to start in a bit that had previously dropped out, why I am not sure yet, not looked at the file closely but I suspect some artifacts in the original drawing. Anyway I tried again with RFH and it failed because of the G31 in macro issue. So again I had to edit the code and it ran the rest fine.
If Set Next Line works then it will work out ok.
As for "lock-outs" then as said all problems so far have been on new starts so not an issue but I do also have the option of pressing a button on my panel which will lock the miniTHC from doing anything until I release it via the button, so that could also be handy.