Recovery 1 - save recipe to file
Assuming you were able to find your all.macro file and get an old Foldit client running in Scenario 1 or 2, you'll be able to access the cookbook.
When you hover over a recipe, you'll see a notepad icon with "Edit recipe" as its hover text.

Clicking the icon opens the recipe editor. The view shown here is condensed for space.
A Lua "V2" recipe has "ScriptV2" in the title bar. This is the current version of the Foldit Lua interface. Most V2 recipes should have imported normally.
The "Save As" button at the bottom of the recipe editor is also important. It's the first step in saving a recipe to a file.

Lua V1 recipes have "ScriptV1" in the recipe editor title bar. These recipes are no longer supported in Foldit. Using the old cookbook editor, they can still be saved to a file. They can then be converted, either manually, or using a program written by @Rav3n_pl

GUI recipes may also be found in the cookbook. These recipes show "GUI" in the title bar, and look very different than Lua recipes. GUI recipes can't be saved to a file. A Python program is available to convert them to Lua, however.

The "Save As" button gives you a recipe's current name and description. For Lua recipes, the "Export" button lets you save the recipe to a file. ("Export" is not available for GUI recipes.)
Highlighting and copying the recipe's title makes the next step easier.

After clicking "Export", you'll see a standard "Save File" dialog for your system. The Windows version shown here has been trimmed down quite a bit. Locate good spot for your recipe, maybe creating a new folder "Recipes" under My Documents on Windows. Then paste the copied recipe name into the "File name" box, and add the extension ".lua" to identify the type of file.

When you click "Save", you'll have your own copy of the recipe's source code. For V1, that code will need to be modified to work on the new system. For V2, all that's needed is to start a new recipe on the website, then paste in the recipe's source code.
On Windows, Notepad can be used to open a ".lua" file. If you just click on the file, you'll be asked which program to use. Select Notepad, which should appear in the list. You may also want to click "Always use this program to open…" to make the association permanent.