Or they could just re-cast his character.
I remember reading that they re-cast the actor who played George Burns' neighbor on "The Burns and Allen Show". Before the new guy's first scene, George interrupted it and turned to the audience and told them that a new actor will be playing the character as the other actor wanted too much money and went on to give the new guy's cue line.
Or, they could do what "Mary Hartman, Mary Hartman" did and explain the new actor by saying that the character fell into a vat of Rustoleum at work and he looks completely different since they took off the bandages!
"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