Illness: credible fear of deterioration permits omission followed by make-up. Travel: a qualified traveller has a concession; fasting is preferable if harmless. Death while the excuse continues: no opportunity for make-up and no ensuing liability in that case.
Recovery or residence before death: proportional liability. Scheduling: separated or consecutive make-up is allowed. New Ramadan: perform the current month first, then the older make-up; no extra Hanafi fidyah merely for delay.