MiniMatt

Like Stu says, it's the interior lining that's the "one hit" bit, not the shell. The important bit in a helmet is the EPS foam, it's the stuff that slows your head as it travels toward the inside edge of the shell. It's not a spring, it's a one-hit-wonder, it gradually compresses and releases that energy as a teensy bit of heat. It doesn't return again, ergo, once it's used it's used.

Despite the shell material receiving the most marketing (kevlar/titanium/made-upium composite etc), all the shell really has to do is protect against abrasion (which any shell material can do very well) and piercing (which, in real world accidents is very rare).

As such, with nothing in the helmet at the time to compress the EPS, assuming the shell survives (which if it didin't needs sending back ASAP anyway as something's seriously wrong if it can't), then I'd think it'd be fine.

Obviously this is all my opinion, so don't blame me if things go wrong, but I'd probably wear it without hesitation.