Great questions. Here are the answers:
I have swamped the tube and the issue follows the tube. I get no current when trying to bias and the tube does not get warm has a burn spot on the its side unlike the "hot spot" of 3 other tubes.
Rogue Audio said it is okay to operate the amp with the dead tube. It is inserted. I turned it off at first until they advised it was okay.
I finally tracked down a KT120 for sale. I'm now thinking to buy 2 KT120's and get the 3 remaining working tubes tested. Set the weakest aside as a spare. Delivery on a new tubes will be 3 weeks. 🙁 Getting the tubes tested is also not trivial as the nearest shop that I know of is an hour's drive away. I will keep looking closer to home, but I live in rural Ohio.
I like the idea of a full set of KT88s sitting in a drawer. That may be a Christmas present to myself.