I'm sure Russia is willing and able to defend SA from iran and others if us pulls out...
After Ukraine there's serious doubt on the able part.
There's also the problem of SA fighting russian supported forces in Yemen.
As for SA, their army is even more corrupt and incompetent then russias, if US pulls out we might see them toppled or invaded easily. (regime change might be a good thing though)
You're also fast to proclaim petrodollar dead... everyone printed as much as the US or more.