There is scant evidence that Glass-Steagal would have made a difference.
Glass-Steagal would have prevented the AIG mess, which is what really made the melt-down cause government intervention.
The government was content to allow Lehman to go down in flames. That roiled the commercial paper market something fierce, but the government was still content to sit on the sidelines.
When the AIG exposure came to light, however, then the government jumped in with both feet. And AIG was able to do the stupid-on-steroids that they did because of Glass-Steagal being removed.