I don’t think drivers dying makes them more rated, it might add to the mystique a bit in the case of guys like Clark, Rindt, Ascari and Senna but they were all considered great drivers before they died anyway. However I definitely think that in the case of Senna and maybe with other drivers too, the fact he died means some of his fans and people discussing great drivers do not take valid criticism of his driving well at all, or choose to gloss over/ignore their failings as you shouldn’t speak ill of the dead.
I’ve frequently seen people castigate Schumacher for some of the things he did on track, but with Senna they are prepared to overlook what he did in Suzuka 1990, or some of his other more questionable moments.
If you go onto some forums or websites and utter a word against Senna you will get your head ripped off, but I guess that’s as true today for any of the current top guys. It’s probably why Alain Prost refused to speak about Senna for such a long while after he died, he couldn’t really win whatever he said. If he said good things people would be saying he didn’t behave that way when he was alive, and if he badmouthed him then he would be criticising someone who can’t defend himself.