Tbh, don't think he wouldn't have seriously challenged Froome anyway. It surely would have been a much more enjoyable Tour, he might have got a podium or a stage somewhere along the way, but I just don't think he still had it in him to compete with Froome at that point. Like, 2017 Vuelta Contador has become this somewhat mythical figure, but even then he was only actually competitive on a very specific sort of climbs and profited a lot from getting much more freedom because he lost so much time early on.
If you want to be sad about a missed chance, be sad about 2014 and who knows, maybe 2015 would have worked out entirely different without the giro. But at that point he was simply already on the decline.