If the final six veto of BB13 stays the same but the duos never return, Rachel still wins the season.
F6: Rachel was the one to win the veto in real life and still does, Jordan goes 2-1.
F5: Rachel still wins HOH, Adam still wins POV, Kalia still gets evicted.
F4: Adam still wins HOH, Porsche still wins POV, Porsche evicts Shelly over Rachel as Porsche and Shelly never really got along all that well (and supposedly Shelly had convinced Kalia to backdoor Porsche before Lawon volunteered to get evicted at the Lawon boot).
F3: Rachel still wins HOH and takes Porsche, beating her 4-3.
All the duos twist did at 6 was make Rachel's path to the end slightly easier and get Shelly out two rounds earlier.
Jasmina Yeah the only way Shelly really has a shot is if she can get Porsche to take Rachel out at 4. Even then, she likely needs to win the final HOH to possibly win.