I think this definitely would (have?) been an issue, and "priced in," at least to some extent.
OTOH, it's not just rule of law that might restrain the king. It's not in his best interest to cause a run/devaluation of shares in his kingdom's wealth.. in some senses in the crown. International corporate capitalism 1.0 was long-lived and happened while kings still had power... parliaments or not. It's not impossible Aramco could find some equilibrium.
Anyway, even just internal Saudi money could amount to a lot. A little bit of international billions would help boost their trust. I think it comes down to execution mostly, whether or not it happens.
Couldn't ask for a better time, macro-finance-wise.