Seras would probably have suffered through things for a few more years before walking out in the middle of the night - she wouldn't have had diamonds for income or any form of financial support from family (as I can only assume all those 12 year old trainers do), but she'd probably have stolen enough money from her family out of desperation to last until she'd found a new job. I expect that she would have settled down wherever there was decent pay, working hard and saving towards that dream of one day traveling the world.