Unable to compile level blueprint after deleting a structure that was being used as a variable type

After compiling, the variable disappears from the variable list which prevents the user from deleting it and being able to recompile the level succussfully

Not a regression as it occurs in 4.18.1 at CL 3737791 and in //UE4/Main at CL 3738969

The variable NewVar_0 declared in  Untitled  has an invalid type Structure

1. Open up any project in the editor
2. Create a new Blueprints->Structure asset
3. Open the level blueprint
4. Add a new variable
5. Change the variable type to the structure you created
6. Compile the level blueprint
7. Force delete the structure you created
8. Open the level blueprint
9. Compile

Result: Error compiling level blueprint and the variable has disappeared from the details panel

Expected: Able to compile level blueprint or at least delete the invalid variable.