The main intent with deleted product codes is to make room for newer models, which may or may not be direct replacements for the models in question. The following is a list of models being removed from GW Stock, apparently these items are currently available whilst stock lasts.
The following list is from Dante and starchild over on Warseer. Im not quite convinced this is solid, so take with a little salt, until varified. It is at least probable that these models are moving to "direct only" to make room for new models.
9906010133001 - Terminator Librarian - 48-43 - DELETE
9906010139201 - Space Marine Scout Sergeant Telion - 48-53 - DELETE
9906020113001 - Sorcerer Of Chaos - 83-36 - DELETE
9906020121101 - Khorne Chaos Champion - 83-58 - DELETE
99110104103 - Eldar Swooping Hawks - 46-26 - DELETE
99110113019 - Tau Vespid Stingwings - 56-20 - DELETE
99110205126 - Dwarf Hammerers - 84-21 - DELETE
99111466007 - Sauron - 05-13 - DELETE
9906010107201 - Space Marine Apothecary - 48-39 - DELETE
9906010132901 - Space Marine Librarian - 48-37 - DELETE
9906010139501 - Crimson Fists Pedro Kantor - 48-55 - DELETE
9906010143101 - Njal Stormcaller - 53-35 - DELETE
9906010407401 - Eldar Avatar - 46-46 - DELETE
9906011303201 - Tau Pathfinder Rail Rifles Squad - 56-45 - DELETE
9906020309201 - Bretonnian Battle Standard - 82-40 - DELETE
9906020406001 - Wood Elf Waywatchers - 92-39 - DELETE
9906020406101 - Wood Elf Tree Kin - 92-44 - DELETE
9906146300601 - Elf Spearmen - 05-41 - DELETE
9906146401701 - Guards Of The Fountain Court - 05-92 - DELETE
9906146407801 - Aragorn King Of Gondor Ft & Mtd - 04-35 - DELETE
9906991503701 - Fiend Of Slaanesh - 97-38 - DELETE
99110208048 - Ancient Scar Leader Kroq Gar - 88-10 - DELETE
99689999038 - Black Box Orcs & Goblins (Japanese) - DELETE
which as we know happens now and again. These items are currently available whilst stock lasts.
What I found of interest was The Avatar and Terminator Librarian, which hints at Eldar and a previously mentioned multi part Librarian plastic kit.
The main intent with deleted product codes is to make room for newer models, which may or may not be direct replacements for the models in question. This frees up retail space at brick-and-mortar GW & independent stores.
There are some models on that list which are long overdue for being sacked. The Chaos Sorcerers for instance-- horrible models imho. However, that product code doesn't match up with the codes on the GW website.
The deletion of Swooping Hawks is interesting, since the product code is for the actual box set, not the blister pack. Again, it's most likely a move to save space, since the blister packs will still be available.