Seriously, even irl people just have this ridiculous justification for entitlement. As if the world owe them something.
Okay she leaves after Sohan considered adult and can take care of himself. Yes she might be suffer living in that hell hole. However, in the end she's a mother. The least she can do is not leaving her son with that abuser. She can leave with her son, yet she only choose the way out for herself.
I wonder why Sarah didn't save him from his illness. With her knowledge and technology, she is able to bring him to health. Maybe at that time Sarah didn't find his absent will bring her yearning. Only after he's not present she started wanting him and try to make replica of him.
Also, Sohan truly is a pitiful character. He did his best just to live with no complaint and grudge for everything bad happened in his life. He payed the debt he should never be responsible for, let the happy life of a mother who abandoned him, and gave company to a stranger whose existence is just selfishness (Sihwa never try to be considered for him, yeah I know he's an alien that is not smart in EQ aspect). He's a nice introverted guy. He has litte social ciricle. Sadly the closest people in his life just acted by their own interest, never properly care for him. Even he knows his dad is a dead-beat, he can't let him go because deep down he didn't want to be alone in this world. His heart is too kind for letting his mom to live the life she wanted. I'm proud of Sohan when he express how Sihwa is not a joy in his life, because it is the truth. So far Sohan only following Sihwa's rhythm that is too demanding. Please don't make Sohan apologize to Sihwa because he's telling the truth.
I truly feel the pain for him. He's willing to be used just for a slight feeling of company. He is not mentally broken because he has strong will to survive. Sadly for this hard working guy, he has only selfish people that is closest to him.
I don't think her technology could bring him back from the dead, or cure him. Their technology couldn't even make Si hwa maintain the phenotype of his dad, so there's no way their technology could fix the disease.