Coincidentally enough, the exact chunk of Help Island that is missing is the one that was directly under the Test Track ramp.
Which also got nuked and there is no trace of in my inventory.
It's the bit near the freebie store.
Edit
I've erected a temporary granite wall to help prevent newbies from rezzing vehicles and driving off into Orientation Island and getting stuck.
I've rezzed about 3 (possibly 4, I forgets) llTargetOmega() prims with a script cycling llGetObjectName() and llGetObjectDesc() to llSetText() informing passers by that rebuilding work is in progress.
Rather than try and recover TestTrack 1.0 from the database, I rebuilt the track from scratch as a modularised "TestTrack 2.0", using up as much of the horizontal space in the plot setup by Jeska (rebuilding work halted at the construction of the safety fence stage due to the grid being closed).
The Volunteers would rebuild the missing chunks of Help Island ourselves, but we don't have access to the textures used (and I thought it more prudent to rebuild the test track than setup OGLE).
New Edit
I'm pretty sure other chunks disapeared- small props mainly, nothing as obvious as the prim land and wall- which as far as i know still hasn't been fixed .