"People can't go on indefinitely and at some stage they have to retire," said the Ireland hooker, who also stressed that his side have enough ambition of their own without wanting to win a potential swansong title for their former captain.
"But the good thing with this Ireland squad now is there are so many young players who don't fear anything.
"If you tell them tomorrow that Brian isn't playing they'll say, 'that's a shame, he's a cracking player', and they will move on.
"Some of the older guys like me who have been part of Ireland teams where Brian has bailed us out time and time again, it would maybe affect us differently, losing a talisman like that.
"But you see the way he's playing now when he came back for Leinster, and you would envisage it will be the same this weekend for Ireland.
"While he is still playing well, he is still the best 13 we have, so play him until maybe he's not or he decides he's had enough.
"Only one person will be able to answer that, and that is Brian.
"Regardless of whether it's his last Six Nations or not, as a player group we want to win things and I don't think it gives us any extra incentive.
"We know what we're going to get from Brian from the way he plays on the pitch and the way he leads off it and I don't see that changing, whether it's his last season or not.
"I look around the group we have and there are a lot of people who have won things and a lot who want to win more. That's not going to change whether it's someone's last campaign or not.
"I haven't really thought about life without him around. In the past when it has been talked about, not necessarily by himself, he has always been there and always played. He is such a talisman."
"It hasn't got nasty," added Best of the teams' rivalry. "We've just been on the wrong side of the results in the last three games and we're not happy about that."