as stated the answer to my question from other people probably will contain spoilers so if you don't want to know anything about this subject please stop reading this thread now.

My question is when you get given the last quest from the you know what guild and get told to do something with it. If I do do this thing will that be the end of the key for good or will there be something that happens and I'll get it back again.

Just a simple answer of yes you will get it back or no you won't will be a good enough answer for me

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Thanks for that.

Oops, Sorry I forgot about that.

If you're in the TG you don't need the thing anyways. You can get piles and piles of lock picks from the fence down there.

You'll never get the Skeleton Key back after the quest. In order to keep it, you have to not complete the quest.