Not all Imperials weant to Jakku. One Star Destroyer, the "Undetectable" did not follow the rest to Jakku. Instead the ship's crew followed their Captain's order and avoided the planet, and the ensuring battle.
The Star Destroyer roamed aimlessly for a few months out of the New Republic' territory, but as more and more Star Systems joined the New Republic they knew they couldn't keep it up, so to not attract the attention of the New Republic they retrofitted their Star Destroyer as a Mining vessel as most of the ship's crew, including her Captain, came from mining planets and had experience with mining equipment. The ship was renamed the "Alderaan".
Operating as a Mining vessel, they roamed asteroid fields collecting minerals they came across, and then selling them to the highest bidder. They managed to get so much minerals so quickly by "cracking" asteroids with the Star Destroyer's tractor beams. They would either drag small steroids into a modified hanger, of use the tractor beams to pull apart larger asteroids.
Business was good, the Crew were well taken care of by their Captain, and with the money they got from mining they continued to modify the old Star Destroyer's old systems, such as increasing the range and power of their tractor beams.
One day the Captain was approached by an old man who said he knew the location of a planet that no one else knew about. He stated the planet was rich with minerals, and was a "Dead" planet, meaning it had no life. The Captain accepted the offer and paid the old man handsomely for the information.
As par regulation forced on them by the New Republic, they had to inform the New Republic of their business and so they told them of the planet that they were going to mine. They were given clearance and they weant into hyperspace.
At first the "Alderaan" kept it's New Republic over watcher's up to date on their day to day business. On day 82 they informed their over watcher of a discover of some type of structure, and on day 95 they missed their up-date deadline. The Over Watchers waited 48 hours before sending a maintenance crew escorted by New Republic Soldiers to see what was up. They lost contact with them as well shortly after the ship confirmed docking of the Alderaan.