I would think Crombie would be strongly favoured in a Milton by-election. Due to changing demos, it is a more Liberal riding than anywhere else in Halton now. But if she can't win a low hanging 905 seat like Milton (and Crombie is seen as the Liberal's best hope to win back the region), there may be calls for her removal. But, it's not like they have anyone better though.
The one issue that might hurt Bonnie Crombie here is Highway 413. I think she opposed the highway if I'm not mistaken? My guess is that people of Milton (and Brampton) support the Highway, one of the reasons I think Del Duca did so poorly in the areas around the future 413. The western GTA has not not seen any added KM of highway, despite being the highest growth areas in the country in the past few decades, so I guess we'll see if Bonnie does run here, she'll have to pick a side, and for her, I think the better choice is being for the Highway, because anyone against it from an environmental perspective is already voting for Marit (or Schreiner).
Also, many of Doug's "scandals" the issue isn't the highway, (or housing on the Greenbelt, or Service Ontarios in Staples) the scandals are the backroom deals and his friends benefiting from these changes, and I think the media isn't doing a good job representing that it's not the outcome that people are upset with, it's his "developer friends" raking in the $$$ from them.