Almost 7 million character deaths!
Diablo YouTube channel community poll:
Going by the percentage of deaths above(even though only 4,200 votes this gives an average based on percentage):
7,000,000 character deaths / 1 death(low end of the 1-5 deaths) = 7,000,000 * .72(72%) = 5,040,000 players
7,000,000 character deaths / 5 deaths(high end of the 1-5 deaths) = 1,400,000 * .72(72%) = 1,008,000 players
7,000,000 character deaths / 6 deaths(low end of the 6-10 deaths) = 1,166,666 * .09(9%) = 104,999 players
7,000,000 character deaths / 10 deaths(high end of the 6-10 deaths) = 700,000 * .09(9%) = 63,000 players
7,000,000 character deaths / 11 deaths(low end of the 11-15 deaths) = 636,363 * .04(4%) = 25,454 players
7,000,000 character deaths / 15 deaths(high end of the 11-15 deaths) = 466,666 * .04(4%) = 18,666 players
7,000,000 character deaths / 16 deaths(low end of the 15+ deaths) = 437,500 * .16(16%) = 70,000 players
7,000,000 character deaths / 20 deaths(high end of the 15+ deaths) = 350,000 * .16(16%) = 56,000 players
Low end deaths TOTAL PLAYERS = 5,240,453
High end deaths TOTAL PLAYERS = 1,145,666
AVERAGE TOTAL PLAYERS = 5,240,453 + 1,145,666 = 6,386,119 / 2 = 3,193,059
So, conclusion is based on the percentage of deaths in the poll for each death count the TOTAL PLAYERS who played in the Open Beta was between 1,145,666 and 5,240,453! This includes both Pre-Purchases and non Pre-Purchases since this was an Open Beta!