Pretty sure the amount of helium we could get from nuclear reactions would be quite small. I haven't run the numbers for fission, but I did for fusion, and the helium that would be produced even if the whole world ran on fusion came out to a tiny fraction of our current usage.

It's true that we won't run out completely, but reducing the supply by orders of magnitude could well be a big deal. We'll have plenty for a while from natural gas, but at some point we're going to have to stop extracting all that fossil fuel, and that will interfere with helium production too.