Go to the Department of Labor webiste and you will find answeres to questions that may arise here. I am bothered by this action. Did your father have the right to request FMLA? The DOL says "The Family and Medical Leave Act (FMLA) provides certain employees with up to 12 weeks of unpaid, job-protected leave per year. It also requires that their group health benefits be maintained during the leave." The reduction of hours may be a qulaifying event for COBRA, but many companies keep employees on during surgery as long as his job has not changed. You need to consult a lawyer or at least contact the DOL about this. http://www.dol.gov/dol/contact/. MOre facts need to be developed. Good luck on working through this.
More facts need to be known so do not rely on comments here until consuting with an attorney that practices regularly in this area of law.