I suspect, as said above, that the hooligans will all be locked away for the duration of the World Cup.
It is up to the FA to decide whether to withdraw, and I think that decision would only be made on the grounds of safety.
I don't actually think there would be a problem there. For various reasons.
Pressing for the thing to be moved away from Russia altogether and held the following year, as My Kinnock suggests, would be a better idea. But there is no way that will happen now, Should have been done ages ago. Too late now, and why should sports fans pay for the dillydallying of the politicians.