Neither Tesla nor PIF has commented on the rumored talks. Reuters noted on August 11th that the Saudi Arabian fund wasn't actively involved in backing Tesla's potential move, but that didn't rule out talks.
It may sound odd for the Earth's largest oil exporter to back a company that would ultimately undermine its main industry, but the source indicated that this dependence is precisely why Saudi Arabia would want to help. The country reportedly sees its investment in Tesla as a "hedge" against its oil business. It wouldn't have to worry quite so much as countries back away from fossil fuels and deprive it of its primary source of revenue.
The challenge would be amassing the amount of necessary cash. Elon Musk previously said he had the funding lined up, but it's estimated that he'd need $60 billion. That's no mean feat for most companies, especially one that may still take a while to return to profit. Tesla would have to convince Saudi Arabia and other investors that brighter days are just around the corner, and that recovery isn't exactly guaranteed.