Look at the age of a few of them. Thinking of Sam Herd. He has to be approaching 80 (if not already 80). Seems he was already slipping a bit mentally. His health is not good. Of course, they don't have to replace anyone who dies as there is no specific number required. But the fact is, they will all continue to age and eventually become infirm or even die. So yes, they'll have to be replacements. . . . .
. . . . unless, of course, Armageddon really is right around the corner!