Most areas of the US the apple trees are in dormancy. If the other trees near it are resistant, you might be able to save the tree. let it live for a year then topwork to something else possibly. Prune out the dead stuff until the bark looks good. Seal the cuts. Spray copper based chemicals. Bonide copper works well for other issues. Never had freblght yet.
IF the neighbors are fireblight prone too, probably best to remove, but still spray neighbors when dormant. 2 or 3 trees away if not all in the area.
I use the copper for peach leaf curl when dormant. i use the remaining spray for CAR prone apple trees in the orchard. Tons of trees out there, a good number of them are pretty disease resistant.