In the 1v1 arcade mode, what happens when both players die at the same time? Is it even possible for the players to die at the "same time"? If it is possible, how is it counted in terms of the best of nine rounds?
Yes it is possible for both players to die simultaneously, which results in a draw for the round. It's also possible for time to run out on the round, resulting in a draw. However, these rounds aren't counted towards the maximum nine rounds per match. In fact, don't even think of it as a best of nine, think of it as first to five points. If the match is tied 4 to 4, and as Mei (other characters are possible too) you both land an icicle killing blow, the round won't be counted, and you'll go into a new match point round with a new character. The round that ended in a draw won't even show up in the end game summary.