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 ?
Um, do it at your own risk because your transaction might get stuck for a very long time.
That depends on what you consider to be low fee, a fee of 20 satoshi/byte will give you a confirmation in about 10 hours if you are not in any hurry to get a confirmation and you are sending this to a friend then that is a good enough fee, in the other hand if you need a fast confirmation then that will be a awfully low fee.