Hopefully I’m missing something, but I got frustrated again today when I accidentally saved a customization that failed compilation. As I understand it, there’s no way to recover this revision.
And if that’s the case, why am I allowed to save it? It shouldn’t be an option.
If you open it in developer mode and select the customization, you can go in and comment out the error. Save and reopen, the UI customizations should then be back.