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 ?
Doing transaction without miner fee will be impossible thing to happen but paying low fee might take your transaction to a very long time of wait. Because miners perspective that if you pay a large fee, that transaction might be urgent or an important one that's is why you are paying a large quantity of transaction fee.
Yes your money must return to your account upon pulling out your money from the pool. But if you want to assure that your transaction will be process, pay the right amount and take a lot of patience upon waiting.
What's this about pulling money out of a pool? Your coins are "returned" once the network forgets about your transaction. This happens when nodes stop re-broadcasting your unconfirmed transaction (by default 72 hours but it could be configured to anything).
Alternatively if you have a bitcoin client that allows you to double-spend you could also try to double-spend those coins with a higher fee. If that succeeds, then the previous transaction becomes immediately invalidated.