I have been working on compiling composite season results for men's and women's teams for a a while now (I have more men's seasons) and for last season I come up with 120 women's regular season overtime games, 45 wins and 75 ties (counting the Beanpot championship game as a tie) for 37.5% of games having a winner. I have uploaded a
workbook with men's overtime games for 1975-76, 1984-85, 1986-89 (all 10-minute overtimes except for CCHA league games in 88-89), 1998-99, 2008-09 and 2012-18 and women's overtime games for 2015-18. As the overtime rules are for both men and women I have also combined the 2015-18 numbers for overall NCAA totals. For the past three seasons the combined win rate for overtime games has been 35% and if you go back to the 1988-89 CCHA games the average win rate for men's overtime games for the season's I have is 35.78%, with individual seasons fluctuating between a high of 41.38% (1988-89 CCHA) and a low of 31.18% (2016-17 - the women had a low of 30.53%). I still have to compile more seasons, especially for women's games, but it appears that only about 1/3 of overtime games have a winner with the 5 minute overtime. Compare that to the average win rate for men's overtime games through the 1988-89 season (excluding CCHA games) of 66.1%, or 2/3 of overtime games having a winner.
Sean