What are you trying to imply here? ^^°I say no, so don't do it. Stay with 'long gone'.
When you ask Can ... be used?, I presume you're asking if we think you should use whatever it is.
Can you name an example? I also have one for you: "While my drug using days are long gone by I wonder if having taken them caused me to not be able to turn back because I’ll never forget how these things had made me feel."In some contexts, yes. I don't think you can say it would work across the board.
What are you trying to imply here? ^^°
"While my drug using days are long gone by ... "
I noticed that this has lead to some misunderstandings but a lot of the sentences I could derive from my actual chats with people are about very controversial topics, even more so than the drug one so I need to come up with entire fictional dialogue before making these posts which I struggle with a bit.This is actually a decent example, where I think you can get away with it, since the phrase gone by collocates strongly with days. In future, please provide a complete sentence in post #1.
I think your observation is right and I will write them down as separate vocabulary(?) now.The reason I'm saying this is that it seems to me you may be confusing 'long gone' with 'gone by'. Get those two phrases clearly separated in your mind first before you try to fuse them together.