While that's true and he is great, we have to also remember that the longer you postpone replacing him, the closer you get where you will be forced to replace him. Wouldn't it be better to replace him while he is there, so like keep playing him for 70 minutes or so, but because he is old, he will get tired after a while, and find the next player after Ronaldo and give him time now. I do not know much about Portugal national team, but isn't there some 18-20 year old striker who has some potential? That way, on the last 20-30 minutes of each game, play that 18-20 year old potential player, this would be better.
The last time I watched a Portugal game without Cristiano Ronaldo playing, they couldn't attack their opponent untill Cristiano Ronaldo was introduced. I think what make the coach play him more, is as he give the players motivation to play for goal and not just passing the ball around without any direction. There has been some game that Portugal played and won without Cristiano Ronaldo but when he's on the pitch, the pattern of play is different and more direct as he's a perfect target man that you play the ball into the penalty box and be sure that he's going to attack and potentially score a goal. But I support you that Ronaldo needs some rest and should play less minutes