Cloud of inert gas? It doesn't have the same impact as "inert gas bag"
Helium is by definition one of the inert gases also called the "noble gases" - Not insulting. "noble gas :- any of a group of rare gases that include helium, neon, argon, krypton, xenon, and usually radon and that exhibit great stability and extremely low reaction rates —called also inert gas" - Merriam-Webster dictionary.
A cloud of gas could disperse. Those who don't like "gas bag" would not like that either, as it implies that God would desert them. The alternative meaning of "longwinded speaker of empty words" is mild as an insult compared to some of the things hurled at God.
Anyway, God (if he exists) has a sense of humour.