I suppose it's going to be a while before we run out of alpha emitters. So the Wikipedia page is wrong then, when it says Helium is a finite resource. Last time I trust Wikipedia (yeah right:).
You said it slowly dissipates into space. That means the rate it leaves the atmosphere is low, so the rate it is replenished is low, and that's the limiting extraction rate.
According to
this (that didn't take long), the rate Helium leaves the atmosphere is 50g/s, or
3e5 cm^3/s. The
National Helium Reserve is 1e9 m^3. So, extracting
all of the Helium from the atmosphere before it escapes, it would take 1e9 m^3 / (3e5 cm^3/s), or
over 100 years to replace the reserves.
But extracting all of it is hopelessly unrealistic. I don't know, but it seems even 1% would be ambitious. So now we're looking at tens of thousands of years.
So either the national reserve is ridiculously large, or removing it from the atmosphere is not going to be a solution to the shortage. Right? Or am I missing something (else)?