Sub-Zero is a very experienced and seasoned warrior. He has been fighting since MK2, and has overcome lots of obstacles in his career. He fought Smoke, defeated him and reprogrammed him to help him fight Cyrax and Sector. The 2 cyborgs were defeated. In Deception he was ambushed by Tarkatans in the living forest and ended up slaying them. Only being that has managed to outright beat Sub-Zero is Scorpion, and Scorps is not an opponent to be underestimated.
Current Sub-Zero's status:
In Sub-Zero's Armageddon ending, after the defeat of Blaze, he attains God-like power. This, combined with his power from the Dragon Medallion, Sub-Zero became so all powerful that he became an Ice God. This however, was without the consent of the Elder Gods, who responded by sending their Champions to destroy him.
An example of the Dragon Medallion's power increase would be when Frost stole Sub-Zero's medallion in her Deadly Alliance ending. She used it, and her powers increased so much that she could not control them and ended up being frozen by her own powers. Go figure.
Ayane is dead...except she is lucky he is a force for good, and therefor he would not actually kill her.