Wait just a minute.

[Dannyalcatraz]

Should't it be mango-kitten chutney?

 

[jefgorbach]

No. Supernatural abilities describe inherent traits of the creature, not possessions - thus the balor's ability bestows the vorpal-property to its whatever sword the balor/you happen to be wielding at the time; releasing the sword removes that temporary property.

IMO the ability works with any handheld weapon which could feasibly sever the foes head, be it an axe, polearm, sword, or etc. It merely states "sword" because those are the balor's weapon-of-choice.

 

[Ahnehnois]

If your DM lets you freely use and abuse shapechange and all you do is generate unlimited money, he should be breathing a sigh of relief.