Sorry for the loss. Many questions to ask here.
First, what size is the system ? Large Angels need systems of at least 180 Gallons IMO
Here is a chart to give some basic guidelines on tankmate possibilities.
What were the results of the water tests?
If the main tank was treated with meds, were measures taken to remove them, such as large water changes and running GAC
How old it the tank? Large Angels should be put in a mature stable system.
How much live rock and what kind of filtration are being used?
These are just a few of the questions needed for us to advise if keeping an Imperator again is a good Idea or not. Beautiful fish, but has some system requirements and demands some special care. Here is some good reading on this species, be sure to go through the FAQ
's at the top too.