As cptskippy said, the helium is at atmospheric pressure, so a leak would not fail catastrophically. Helium would more or less slowly diffuse. If the leak is sm

As cptskippy said, the helium is at atmospheric pressure, so a leak would not fail catastrophically. Helium would more or less slowly diffuse. If the leak is small enough, helium could get out but larger molecules would have a harder time. Thus the pressure inside the enclosure would get slightly lower than atmosphere and leaking would slow down. The iPhone MEMS failed when a rather large amount of pressurized, cryogenic helium was leaked during an MRI machine servicing. The quantity of unpressurized helium in a tiny HDD enclosure is minuscule, and thus the slow diffusion is unlikely to register above background levels, even at very close range.