D&D Beyond will be permanently removing Volo’s Guide to Monsters and Mordenkainen’s Tome of Foes on May 17th in favor of the upcoming Monsters of the Multiverse book, which largely compiles and updates that material.
As per the D&D Beyond FAQ for Mordenkainen Presents: Monsters of the Multiverse:
If you already own these two books you will still have access to your purchases and any characters or encounters you built with them. They won’t be removed from your purchased sourcebooks. Therefore, if you want the "fluff" and tables in those two tomes in D&D Beyond, you need to purchase them soon.
This is the first time books have been wholesale delisted from the D&D Beyond Platform rather than updated (much like physical book reprints are with errata and changes).
There’s no word from WotC on whether physical books will be discontinued and be allowed to sell out.
As per the D&D Beyond FAQ for Mordenkainen Presents: Monsters of the Multiverse:
Can I still buy Volo’s Guide to Monsters or Mordenkainen’s Tome of Foes on D&D Beyond?
Starting on May 16, you can acquire the streamlined and up-to-date creatures and character race options, as well as a plethora of exciting new content, by purchasing Mordenkainen Presents: Monsters of the Multiverse. On May 17, Volo's Guide to Monsters and Mordenkainen’s Tome of Foes will be discontinued from our digital marketplace.
If you already own these two books you will still have access to your purchases and any characters or encounters you built with them. They won’t be removed from your purchased sourcebooks. Therefore, if you want the "fluff" and tables in those two tomes in D&D Beyond, you need to purchase them soon.
This is the first time books have been wholesale delisted from the D&D Beyond Platform rather than updated (much like physical book reprints are with errata and changes).
There’s no word from WotC on whether physical books will be discontinued and be allowed to sell out.