" Rapidly decompressing, rapidly expanding...
As they inflate, their volume increases.
With higher volume come less density.
Less density means more buoyancy.
More buoyancy accelerates their ascent.
The higher they go, the less the external pressure.
And the more they expand. A vicious cycle.
They've reached the point of no return. Even if by some miracle their equipments could function again, it couldn't vent out the pressure fast enough. Even combined with their spewing and leaking. Their bodies would lose the water before they lost the helium.
Ever higher they float, up the water column until sunlight begins to beam down, a signal that they are reaching the surface. "Second part, rising up to the surface and getting closer to their bursting point! How big would they be when they reach the surface, if they even get there at all?