First, I want to emphasize that I realize this problem is 100% my own fault for not being more careful and a) backing up the site and b) reading your description more carefully.
I installed Dashboard Widget Order and now I'm locked out of that site and can't remove it. Luckily it's my "sandbox" site where I play around with things. If I delete it and start another sandbox.
I'm writing to suggest some sort of installation or activation warning that would detect if an installation would conflict with the site.
Again, I realize this is completely, unambiguously, my fault.
One more question. I've got a number of different usernames here. kenn_fong4 is currently the master account. How do I delete the other account(s)? I want to do this because their existence blocks me from using my preferred email address, which is Kenn@KennFong.com.