The legal outcome would be roughly the same, even if it's a double murder(as opposed to the single one in OTL). Those killers were gonna end up doing hard time, no matter what the body count.
If Polanski dies, he's probably remembered mostly for Rosemary's Baby, which has an even more sinister rep than what it garnered OTL. Yes, logically speaking, there is no more reason to draw a "satanic" connection from one body than from two, but the death of the director himself is going to have a psychological impact on how the film is viewed(at least among conspiracy and occult buffs).
And occultic conspiracies aside, Polanski will be regarded as more of a "legend", as opposed to the current view of him as a one-time auteur, pummeled with self-inflicted scandal, then sloughing it through a steady artistic decline in exile from Hollywood.