"It's a reasonable proposition to think this might be the last time we see this squad together. Age means some players are nearing the end of their Test careers," said British & Irish Lions assistant coach O'Sullivan.
"After the Lions tour it will be time for less experienced players to make the transition into Test rugby, but we have to make sure the players we are bringing in are better than who we have at the moment."
It will take a big performance to prevent the rampant Welsh claiming their first Grand Slam for 27 years but O'Sullivan believes his team will rise to the occasion.
"Wales have played the rugby of the championship - they've been outstanding right the way through, especially in attack where they have torn sides to shreds," he said.
"They are on a roll and confidence is very high. Wales have always had fantastic footballers.
"It's their national sport and at the moment they're playing like there's no tomorrow. We all had it in the back of our minds at the start of the championship that Wales were the danger team.
"To win in Cardiff, in front of what is going to be a partisan Welsh crowd, is a massive challenge.
"But we believe we can win if we get things right. This Welsh team is going to take some beating but we will go there and given them one hell of a battle."
France are still in the title hunt but O'Sullivan believes the tournament will benefit enormously should either Ireland or Wales finish top of the table.
"It would be great if a Celtic nation won the Six Nations," said O'Sullivan, who has named an unchanged side for Saturday.
"At the start of the tournament France and England are usually tipped to win - and rightly so because they are the big threats if you want to win a Grand Slam.
"But it's great for the championship if there are a few teams battling for the title. We don't want it to become boring where the same teams win every year.
"Wales have made dramatic changes to their domestic structures and are starting to reap the reward. That's great for European rugby."