User blog comment:B214/Question and Answers 6/@comment-24.178.107.246-20160708154011/@comment-24.113.252.213-20160731211012

Was it ever explicitely said that the Boosted Gear only ever appears on the wielder's left arm? It could be that it appears on the wielder's dominant arm. Although if it's confirmed that Issei is right-handed, then that theory doesn't work.

What I think is:

The Boosted Gear is bound to Issei's soul, not his arm. The gauntlet is merely the power of the Red Dragon Emperor manifesting in a physical form. So if Issei's left arm is severed, the gauntlet will likely appear on his right arm. And if his arm is severed while still wearing the Boosted Gear, I bet the gauntlet would just dissipate, since the Sacred Gear is bound to the soul, not the arm.

If Issei could be killed by having his arm severed while wearing the Boosted Gear gauntlet, then by that logic, he should've been killed when his Balance Breaker armor was shattered.