It would be appreciated if the rewards from Online Mode could be accessible in Offline. How it is done is up to you, there are many methods out there to allow a steam game to give access to content within the game.
To name a few, hidden achievements that are unlocked upon claiming a reward, which gives access to the associated content, hidden DLC that is granted upon claiming the drops ect. If the items are ingame and so are the recipes, I don't see why they couldn't be made available in offline mode. Perhaps it would be tedious or require a lot of thinkering, but I do believe that would benefit everyone.
