Welding CO/Argon tank question

Off topic question for you professional (or hobby) welders.
I have just a little experience Mig welding. Have borrowed from various friends when needed and always done fluxcore (I think thats what its called). So never used gas. The projects didnt call for "roll of dimes" look, so it was good enough.
Anyways, my uncle is passing down his Miller 211 to me with his tank and all accessories. Very nice setup and Im looking forward to getting plenty of use out of it.
He hasnt used it in over 10 years though. Do the tanks expire or go bad? Does the gas? I imagine the CO and Argon might just separate. Would rolling the cylinder properly mix it? Its got a date stamp of 2015.
I apologize if these are idiotic questions, but storing gas for over 10 years makes me nervous even though It says non flammable.
He did say his regulator might be broke so is there a way I can tell if the tank is empty? I usually weigh my propane tanks and compare them with the weight stamp on the cylinder. Can I do that with these types?
Thanks guys