User blog comment:B214/Question and Answers 6/@comment-24.178.107.246-20160708154011/@comment-106.68.152.135-20160731153917

It's not about the effect of merely severed arm. This is about Issei's left arm got severed, especially in case when he was equipped with Boosted Gear.

This is just my speculation:

Let's say that Boosted Gear was equipped, then Issei's gauntlet arm was severed. Yes, in that case, Issei was robbed of his Sacred Gear, possibly resulting death in the end.

However, if Issei was not equipping the Boosted Gear on his left arm and the said arm got severed, technically the Red Dragon Emperor's Gauntlet is still stored inside his main body, attached to his soul. However, since Boosted Gear's default setting and appearance was to be used by left arm, Issei will have some trouble in using his Sacred Gear until his left arm is re-attached, or he somehow learned how to manifest the Boosted Gear on his right arm.

Thoughts, everyone?