Is it obligatory to respond to my father's wish for me to return to education and work, and would that be considered a breach of my covenant with Allah and the repentance I made to myself after my mother's passing?

Repenting for negligence in serving your mother does not necessitate leaving your job. The greatest pillar of repentance is remorse. If you feel remorse, your repentance is sufficient. The pledge to leave your job is akin to an oath. Whoever breaks this pledge must offer an expiation for an oath. If the job is permissible, and obedience to a parent is obligatory in matters that do not involve disobedience, and your father has commanded you to return to the permissible job, then obey him; for obedience to parents is obligatory even in matters that are permissible, disliked, or doubtful.