If the doctors can get it unclogged, then there's no problem. Your Dad is in the best place he can be right now. If the vessel remained clogged, blood would be cut off to part of that heart and it would stop working, meaning the rest of the heart needs to work harder to pump blood.
The condition your Dad has is called Angina--a temporary clogging of the blood vessel(s) to the heart. It is NOT a heart attack
and can be managed with medication, diet and exercise.