Is the son's absence from his father, in order to avoid his verbal abuse due to the son's financial situation and inability to repay a debt to his father, considered disobedience (uquq) that warrants entry into Hellfire, especially since the son visits his mother daily?

You must pay off your father's debt, prioritizing it over all other creditors, if you have the means to do so, because not paying when able is an injustice. If you are unable to pay, he must grant you a respite, and it is not permissible for him to curse you, as Allah Almighty says: "And if there is one in [financial] difficulty, then [let there be] a delay until a time of ease." Approach your father and strive to appease him by removing the impediment, which is the debt, and explain your true situation to him. If he sees that you are aware of your responsibility, he might soften towards you.