Yup, to get to the single-elimination rounds, you just have to go W-W, or W-L-W, or L-W-W in the group stage.
The event (for those who didn't have to survive multiple qualifying tournaments) is actually less of a marathon than a standard 128-player double-elimination event. The winner of the W9B will have played either 2 or 3 matches in the group stage and then 6 matches in the single-elimination stage, for a total of 8 or 9. In a double-elimination event, the winner will have played anywhere from 8 to 14 matches (assume a single set in the finals).
And in the W9B, they stretch it out over 7 days, with no match starting earlier than 11 am local time and no match starting later than 6:30 pm. In the group stage, if I read the brackets correctly, 120 of the 128 players will never play twice on the same day; the other 8 players play 2 times on one of the days. In the 3-day single-elimination stage, everyone plays just once on the first day, then 3 times on the second day for continuing winners, and then 2 times on the last day.
So it's a pretty slow trip through the brackets. The players will have plenty of down time and should be well rested for all matches.
