Is a son considered undutiful (aqq) if he abandons his parents due to their ill-treatment and repeated insults, despite his complete care for them, or should he remain and endure?

Obeying and honoring one's parents is among the greatest righteous deeds, and one must maintain this without showing weariness or displeasure towards them. If you wish to discuss matters with them, do so kindly. As for traveling for trade, if there is someone to care for them, then there is no sin upon you. However, you must be gentle with them and present the matter well to them to gain their consent. If you are not in need of traveling, then your staying with them is more preferable and better, so you can attend to their needs. As for abandoning them and turning away from them, that is not permissible.