If experience help players, I'm not sure Ronaldo would lose that penalty that in their Knockout stage for Portugal, he weep his eyes all through he match and was pet by his team mate not to cry, this is happening because Ronaldo is old, he can't be like his prime anymore, anything his doing now is just struggle to fit into a place where he is not supposed to be for that time. I hope Modric don't disappoint the team like that too in the end.
Experience helps in a team. Saying experience doesn't matter in a team makes me wonder how well you understand football. I don't mean the team have to be filled with 30+ players, the team just have to find the right balance with the experience and young players. It has to be a mix of both. When a team is too young they lack experience. There are parts of the game that require just experience. We saw how influential Modric was when he came on in the second half of the champions league last season, experience helps you do that.
Ronaldo didn't miss the penalty because he was old, either he was just unlucky or his technique was poor. It could also be that the keeper did a really good job. Ronaldo missed a penalty in his young age at United, at his peak at Real Madrid, so missing a penalty at the twilight of his career isn't a big deal. Even Messi missed a penalty in his prime.
As long as a player is still good and strong enough to play, his experience will mean a lot to them team.
At Madrid, nobody can do what Modric does, despite the fact that he's old. He's the most creative midfielder they have. He understands to the game better than all of the. He may not be strong enough to run all game and win back balls or compete for duels, but when he has the ball, he knows how to make use of it.
Madrid might do fine without him, but I believe their odds of success is better with Madrid around.