Judging from the discussion in the AL_EXT_disconnect extension, this does not appear to be possible:
Should we make promises about buffer data post-disconnect?
RESOLVED: No.
The AL currently supplies no means to recover buffer data, and all contexts sharing buffers must be on the same device. As such, all buffer data is lost in the event of a disconnect. The application will be required to reupload all their buffer data after opening a new device. If a future extension exposes a means to recover buffer data from the AL, it should amend this specification.
So far I haven't been able to find an extension to recover buffer data. However, it might be worth directing this question to the openal mailing list.
Edit: another relevant discussion on stackoverflow:
All the al* functions (rather than alc* functions) operate on the current context. So, alGenBuffer calls will operate on the current context and create Buffers that belong to the Context's Device (a Context can only have one Device).
Buffers created on one Device are not available on another Device.
A Device's Buffers will (probably) be automatically destroyed when you call alcCloseDevice.