a) OSS is a colocation customer with its own hardware colocating it inside an Iron Mountain datacenter. In which OSS owned the bare metal and paid iron mountain for rack space and power.
or
b) OSS is a dedicated hardware customer of Iron Mountain running a service on bare metal owned by Iron Mountain, and has gone defunct, leaving behind a bunch of servers/storage arrays that would in normal circumstances get wiped/reprovisioned.
From the point of view of a customer of OSS (PBS), that's two extremely different things.
If it's scenario A, I don't see how PBS has any claim against Iron Mountain. Your typical datacenter colo host for bare metal hardware owned by a customer has no involvement whatsoever in the condition or operation of the data, operating system, filesystems, RAID arrays, ZFS, etc of how the customer has set up their environment. Nor any ability to do anything with it. A colocation host that hasn't been paid for its rack space and power will typically have clauses in its colo contracts allowing for seizure and sale of abandoned hardware after a certain period of time.