If symptoms in arm still persist after anterior distectomy with fusion and plates c7 t1 does it mean that there is irreversible nerve damage?

Don't despair. The surgery may well have prevented further damage, but reversal of pre-existing problems may take time. Nerve damage may reverse, if optimal, at a speed of 0.1mm daily or speed of fingernail growth. Physical therapy has some potential, and exercise may restore part of this. An EMG test can tell if there is re-innervation and peripheral nerve sprouting.