There is something funny about both oil and money -- you cannot eat either. You cannot drink either. You can only trade those things for other things that you want.
If the Saudis want to pull their assets out of Western banks, then they have to put their money under a mattress. It does not get them anything there.
Look at their alternatives. They could invest the money in China -- that might be easier to do than to get out of, like the Iraqi jets flown to Iran for "safe keeping" at the beginning of the Gulf War. They could invest them in Arab banks, trading unneeded currency back and forth. They could put them in Russian banks, where the Russian mafia will show them a thing or two about creative financing. Possibly they could put the money in Japan, which would invest it in the west, and keep a finder's fee for each transaction.
I know! They will invest their money in Sub-Saharan Africa. Black ivory!