> Humans die under 10g for more than a few minutes

With no air?

It's not about the air. Its about our fundamental squishyness.

At 10g, a 150lb man would weigh 1,500 lbs. His heart isn't strong enough to move blood that suddenly weighs 90lbs/gallon that also has to push other blood that also weighs that same amount. His blood vessels, paper thin and easily torn under normal weight, suddenly have 10 times the amount of pressure to resist.

He's fine for a few moments, jet pilots experience short bursts of 10g during flights quite often, occasionally more.

Might pass out after 10-20 seconds, but after 10 minutes, his brain, starved of oxygen and squished under its own weight, ceases to function. His heart or his blood vessels rip and tear from the strain, and his body falls apart inside of its own skin.

It's not pretty, but it would probably be a fairly painless way to go.

Getting back to your question, his ability to breathe is not relevant under those situations. The absence of oxygen would accelerate his demise no more than it would under any other situation.