If Masi had decided not to unlap any cars, I still wouldn't have been totally surprised if Max would have managed to beat Lewis over the one lap. I suspect the cars in between would have jumped out the way pretty sharpish.
I believe a red flag and restart would have been the best option, followed by either getting a move on with the SC (the. track seemed clear for quite a while) or simply not allowing any lapped cars to unlap themselves.
I wonder if the race director got into a bit of a pickle with issuing the "safety car in this lap" order before all lapped cars were unlapped (if this did happen - I may be mistaken about that). Rules 48.12 and 48.13 together do seem to have some potential problems when enacted out of order.