With 3 capable HB's, I have to go with the hot hand.
Not only could Montreal be the first team to win 3 World Bowls, but would also do so by having 3 different HB1's.... Phillips in 2005, Welch in 2007 and now Walker in 2008...
Remember Welch filled in nicely for Phillips when he was out for 4 or 5 games at the end of the year. Phillips ran 19 times for 100 yards against SAT in week 15's 20-8 win. Phillps was injured here, and Madre Hill filled in nicely, running 7 times for 28 yards and a TD. Then he went down

All that was left I believe was HB Welch, and FB Ricky Brown. Welch started in week 16 against SAC and did fairly well (26-76 TD rush and 11-94 2 TD receiving) in MON's 26-20 OT win. HB Carl McCullough who proved to be a great special teamer was signed to add depth.
In the FIFL Bowl, Welch again stepped up as he ran 24-80 TD and was 8-86 TD receiving in our 20-14 win over SCO.
If Walker had been injured, I almost guarantee you'd see Welch at HB1

Welch can hopefully retire after this year with a 3rd ring, however we would gladly welcome him back yet again.