Can you clarify what style of garage door this is? I'm aware of two main styles: 1) a one-piece door which tilts upward, kinda like a doggy door, and 2) a door with four horizontal panels that rolls straight up on tracks. The first type has giant springs on the left and right, whereas the latter has an axial spring situated just above the door.
In both garage door styles, it should be the case that once the opener is disconnected, the door can be manually lifted and opened, to get the car out during a power cut. If this is not possible, something is wrong and the door itself needs to be serviced first, to avoid cascading issues.
If you do replace the opener, consider models which have a small backup battery, to operate when there's a power cut. The door must still be in working order, but the battery will slowly open the door using the remote control, as normal. Some openers have WiFi connectivity -- which I think is mostly a gimmick, except if there's an app to indicate if I've closed the garage door or not.