@bcwadsworth, I have given you the code to get a tag containing all of the TE's NBTData. Saving it in your entity is basic java. Read the inline comments.
Also, beware that you will have no way of knowing how to recreate a tile entity just by its NBT data. You need its class, as well as the associated Block's class. So, if the TE is deleted as Hugo said, your item is no longer associated with anything.
@Whov, if you understood the question, the answer is not "Go the <someperson> way." State what you think the problem is and offer a suggestion.
@bcwadsworth, you could get more focussed help here by explaining what you are trying to accomplish with this method you seek.