The most annoying thing about these mid-game crashes is that it almost loads in time with "Rejoin game" for you to actually take your turn and the game be unimpeded.

I suggest that when a player hits the "Rejoin game" button, add some amount of time to the game's timer so they have time to reload the game and take their turn (at most once per round or game). This would mean the game would be almost entirely unaffected by the crash.

In most of my games losing out on 1 round makes winning a very steep climb, even when I'm doing well, losing 6+ mana is a game changer, and crushing when you had a great play ready.