Do you believe there is a chance bigger than 0.0 for Russia to go to war against the US over Iran? Let's be serious.
If, by any chance, Israel were to attack Iran (and I don’t think that’s a realistic option at all), I’m sure Iran wouldn’t be left without the help of its allies, and I mean China and Russia in the first place. Although Iran is under sanctions, China and Russia have no reason to enforce those sanctions, when they themselves are victims of something similar.
Have they done something for Serbia? Have they done something for Irak? For Afghanistan?
Nope, and they won't be entering a war for Iran, especially Russia.
Russia will be more than happy to see Iran under complete sanctions or its entire oil production go bust because Russia needs high oil prices, that's why it wants to trigger as much shit as possible in that region, for them Iran managing to sell as much oil as Saudi Arabia is a nightmare.
China? China will not go to war anywhere but near to its own borders, if war breaks out trade goes down, and they are dependent on it, they will not enter a war in which they have a lot of problems separating allies from foes and translating all of it into exports and imports.
Unfortunately for Iran when war will come, as I highly doubt it will be in the years to come they will find out they are alone, alone with no allies and nobody wanting to risk anything for them.