When a diode is reverse biased, the number of localized charges (deplition region) increases and there is no current flow except the leakage current.But when we remove the battery, do the PN junction comes to its original state?Do the deplition region comes to its original size?

 

Well, it can take some time, because the leakage current will decrease as the the remaining charge decreases. But if you short the leads together removing the remaining charge, yes - it'll return to it's original state/size.

 

In simple words, the PN junction will come to its original state, if we want it do so.