For funsies, I ran 10000 simulations for the end of the season based on current pythagorean estimates.
Here was the Cubs' record distribution:
5% - 100+ wins
20% - 98+ wins
50% - 96+ wins
75% - 94+ wins
90% - 92+ wins
Brewers' record distribution assuming they are August good:
40% - 100+ wins
55% - 99+ wins
75% - 97+ wins
90% - 95+ wins
99% - 92+ wins
If the Brewers somehow revert back to their May form:
4% - 100+ wins
18% - 98+ wins
40% - 96+ wins
70% - 94+ wins
90% - 92+ wins
So while it would help the Cubs out (obviously) if the Brewers turned back into a pumpkin, it seems like the Cubs target number to try to win the division is 100 games.
For reference, the Cubs beat out the current Brewers in 1,989 simulations (19.9%). The Cubs beat out the pumpkin Brewers in 5,969 simulations (59.7).