Using the advanced combat code that was merged into BetterAI, this is what I've been able to come up with so far
(using a warrior to attack another warrior on a forest without the fort bonus, but the defending warrior had 100 hp instead of the 95 hp Stuy has)
15.6% lose 0 rounds (next battle therefore odds are identical to first; 97% chance of winning)
23.2% lose 1 round, 89% chance of winning second battle
21.5% lose 2 rounds, 60.5% chance of winning second battle
16% lose 3 rounds, 32.5% chance of winning second battle
lose anymore on the first battle, consider it a loss.
Crap, I've forgotten how to do binomial expansion...but I think it is a little less than 60%...
TBH, if those were the odds, I think heading SE to that forest hill would be wiser. Even if there is a barb hiding in the FoW to the east, it would have to attack over a river.