I was unable to reproduce this issue in the latest version (4.6) with the information that was given. I am given a error message and I am not allowed to compile. I have a few questions that will help narrow down the issue that you are experiencing.
Quick questions:
What version of the engine are you using?
Can you provide accurate steps to reproduce this issue?
Can you provide a screen shot of the blueprint or a remade version that caused the crash?
Recovery suggestion:
The engine has backup files. You could try going back to a version of the project before the widget started crashing. The backup files are located in your Saved file. The default directory Can be found by going to Documents > Unreal projects > YourProjectName > Saved > Backup