If you have any recovery software you may be able to get it back by going to a past date, going to %appdata%, .minecraft, saves, then take the one that was your world. If not, you cannot recover it. I suggest backing up your worlds every day, just incase.
For cuboid you have to READ THE READ ME! Honestly, Read it all. But to use it, right click with a wooden shovel for the first and second points you want cuboided, and type /cfill (Or Cpyramid, Csphere, Cfaces, etc.) <Item ID>
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I then proceed to use a creeper with the face of notch to defile the next in line.
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Thats not funny.
At all.
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I dont know about the others, though.