So i was thinking if i send a bitcoin transaction without the miner fee or a very low fee what will happen ? would i get the coins back eventually ? or they will just stuck there forever ! and if that happened how to do that double spend ?
Bitcoins never go into space. You will either get the transaction returned or it will be included in a block.
no, there is no "transaction returning" in bitcoin. on paper it MAY be possible but in practice when you send a bitcoin transaction it will stay out there forever until it either confirms or becomes invalid (like by double spending) and gets rejected.
to OP if you want to do such a thing make sure to mark it as RBF so that if you changed your mind you still have an "easier" option to solve the problem.
All the above bullsh*t posts aside your bullsh*t is something entirely new, who the fu*k taught you this? when a transaction doesn't get confirmed after a while it will be as if you never sent it at all meaning it will be unlocked/ back to your wallet.