Designs created in Mail Studio behave pretty much the same way as regular emails do if images are disabled. You should add alt text to your images and plan your design so that a missing graphic doesn't cause problems. Still, we're at version 1.0 so I imagine we can do more about this.

The app handles the HTML part of the email, while the plaintext is entered by the user when preparing their campaign. We won't be of much help there.