Formula 1 will wave goodbye to most of its star appeal when Lewis Hamilton leaves, and that day is only getting closer. No individual is bigger than an entire sporting spectacle, and Hamilton's exit will not kill F1 - but it could leave it severely hurt, and F1 needs a contingency plan.
The marketability of a championship and the attention of fans are not givens, they have to be earned. Trying to do that without a star asset is like taking a knife to a gun fight: yeah, you might have a chance of winning, but you're probably fighting a losing battle.
Replacing a blockbuster driver is difficult but F1's prospects are not hopeless. No one driver can have the same impact globally as Hamilton, but two drivers in particular can give F1 something Hamilton does not: a proper rivalry.