Nitrogen being replaced by helium would actually be fine but for the niggling issue that we need nitrates. There are no heliates (?) to compensate. The name doesn’t even make sense… helium is the sole gas to have an ium end like metals- chemically it’s that meaningless what you call it as an ion…it shines elsewhere though.

For biology, it’s a necessary condition that the environment react with it and it reacts to the environment. Over time the two become deeply intertwined through the process of evolution.

It’s hard to see how that kind of evolution will occur if a lot of the environment is nonreactive.

Survival may be plausible though. There’s been some research showing some bacteria can survive in high helium environments. That’s a far cry from proving something like a bacterium can evolve in a helium environment that’s non-reactive though.

So the question becomes: How much of that atmosphere is helium?