I'm not a big fan of Disney star wars but this has been seen before in the force unleashed he was absolutley wrecked and in the Lost command comics he didn't even have his breathing appartus in the last comic, and when he was getting his limbs attached, the thing I will have a go at Disney for is the fact that It took a smashed chest box and cut helmet to defeat him yet in legends nearly his entire suit was destroyed and he still kept on fighting, he had his entire helmet (neck brace included) gone and still carrys on fighting, he burried himself alive and yet willed himself back from the dead, as for the helmets importance it is still important because some ancient sith from the old republic were so disgusted by the humanity on there natural faces (this also applied to aliens) so they covered them with masks like 'Tulak Hord'
And this is why the EU, in any form, is terrible.