France are probably as vulnerable to Dupont getting injured. Considering how many matches he's likely to have played in the 12 months prior to the world cup, there's a good chance of it happening. He's played 21 matches so far this season, played 1483 minutes.10 is the most important position on the pitch and we will have a 38 year old starter and an inexperienced deputy who is shit from open play.
We will see how best of all time this side is in less than six months.
He played 382 of the 400 minutes of France's matches in the 6 nations.
Toulouse have at least 12 matches remaining this season, probably more like 18. There's French 4 warm up matches, with 4 pool stage, it's 8 matches before the quarter final. It wouldn't be surprising if he hits 40 matches between the start of this season and the quarter final.
If he gets injured, they're in big trouble.
Key player vulnerability isn't unusual, but I'd argue that France are at least as vulnerable as Ireland are.