Not really! Just kidding, just kidding. I love Harry Potter, JK is fabulous. Please don't hurt me!!
I just said that to get your attention so you'd come in to abuse me. This topic would just get lost among the clutter otherwise.
But this topic is actually about the mysterious R.A.B.

Soooo...now that I've got your attention.

I think RAB could be either Borgin or Burkes.
Is either of them not mentioned in the books? That could mean they are dead.
I know Mr Borgin was in the 2nd book when Harry travelled by Floo powder into Knockturn alley.

Mr Burke was mentioned in the 6th book when young Voldemort was visiting Hepzibahs house and looking at his future horcruxes.
But that happened years and years ago, when Voldemort hadn't finished making his horcruxes. So maybe Mr Burke found out somehow and destroyed the locket. He hasn't been mentioned in the early books at all, has he? So maybe he's dead. He would have had something against Voldemort to destroy the horcrux.
Maybe he was chasing up the locket which had maybe disappeared. I don't know. Too many maybe's.

Any ideas and thoughts would be greatly appreciated.