Lewis has won 3 of the last 4 titles. If he carries on winning at this ratio Hamilton Mercedes continue to produce a worthy car who knows where he could end up.
Can't see it lasting, This year alone the Ferrari has been consistently faster and Vettel would still have the lead if it wasn't for brainfarts. Added to that the Red Bull is now much more improved and capable of really pushing in conditions the Merc struggles in. But that's the rub, Lewis lost last year due to engine failures and he has won this year due to Ferrari team failures (plus some very consistent top class driving to optimise it).
He would have walked away in 2012 with the championship with several races to go if it weren't for mechanical failures while in the lead but in that case he may have stayed with McLaren and this past few years would have far more swear-filter spamming.