I actually saw the understudy's understudy, when I saw "Grand Hotel" ages ago. David Carroll was still listed as the Baron, but had basically left the cast because he was dying of AIDS.
I saw the show when his understudy, Brent Barrett, was not available. (Possibly because he was appearing in "Closer Than Ever" Off-Broadway at the time?) I saw the swing playing the Baron and he was incredible. (I can't remember his name at present, but he was Cornelius Hackl in the last revival of "Hello Dolly" with Carol Channing and he appears on that cast album.) He was handsome, dashing, aristocratic and an incredible singer.
I loved the show so much that I went to see it again the next night and saw Brent Barrett play the Baron and I didn't like him as much as the swing. I saw him again when he played the role on tour and he had grown into the part by then.
"A coherent existance after so many years of muddle" - Desiree' Armfelt, A Little Night Music
"Life keeps happening everyday, Say Yes" - 70, Girls, 70
"Life is what you do while you're waiting to die" - Zorba