Marway - I seem to remember hearing somewhere that the role of the Phantom was offered to Mandy since Colm Wilkinson (who it was written for) turned it down for Les Miz and they decided the rocker guy, Steve something, I forget his name, couldn't do it. I don't know why but Mandy turned down, and that's when they got Michael Crawford. I don't remember where I heard that and don't know if it's true.
And I definitely agree that getting Mandy for this concert would be amazing if he would do it. In fact an original cast reunion would be the most amazing thing ever!
<-- Tevye, FIDDLER ON THE ROOF, March 2018