The Tour will survive surely, but probably go thru some hard times. Procycling in general will be viewed very differently by those on the outside - i.e. people who only know/heard about the doping. Unfortunately many of those folks make key decisions regarding TV coverage, pro sponsorship etc.
So expect a very different pro scene over the next decades. I think as the pro teams start to disappear, the grand tours may even have to resort to tier 2-3 teams, perhaps even national amateur teams to make up the numbers, but still retain some sort of prestige that could come with an Olympic or World championship type national representation.