Earlier quoted context omitted.
We don't know. Glass Steagall Act doesn't really deal with the fundamental problem with 2008, which was at its core an error in measuring potential risk of new finantial products. It could have prevented some of the worst impacts of that error, but we're not sure. Here's quote from former Federal Reserve Vice Chairman Alan Blinder: "What bad practices would have been prevented if Glass-Steagall was still on the books…
Wouldn’t Glass Stegall have made mortgage backed securities difficult if not outright impossible to create?
Crisis would happened anyway for sure, but the scale could have been smaller. But it's hard to do what-ifs.