Hardness for a vorpal sword?

[Shin Okada]

Balor's vorpal sword was (Su) even in 3.0e. And AEG has "Balor's Sword of Flame" as an magic item. It was just a magic item. Could be broken, stolen, disarmed, and such.

I think it is still true in 3.5e. In fact, no rule says a magic sword in the hand of PC is not a (Su) ability.

 

[Epametheus]

It looks like you could sunder it by the RAW, yes.

I've always handled a balor's weapons as snapping in and out of existence when the balor wants them to -- the weapons take shape from the aura of fire. So I guess a PC could disrupt (sunder) one of the weapons, but it'll be right back on the balor's turn.