"Degrading" means that the color shifts because of different degradion of the individual sub-colors. Not nice for watching movies. No problem for reading letters. It's not like the whole display will be black and unreadable.
I hope so, but some of the pictures I have seen make me doubt that. 
oled after 5 years mostly unused. I have seen pictures of one colour displays similar to the ones used by trezor that can't display readable text anymore , but I can't find them again right now.