Northern Mang was not destroyed. The ending of Sword Snow Stride " was that the world was at peace, and the Northern Liang protected the gate for Liyang, and the Northern Mang did not trample the Central Plains. Xu Fengnian led his family to live in seclusion in the mountains. The new generation of youths from Northern Liang entered the imperial court of Liyang, and their careers were bright.
The situation of Northern Qi being destroyed in the "Celebrating Years" was not explicitly mentioned. Thus, based on the information provided, I don't know if Northern Qi has been destroyed.
Beiliang and Beimang were enemies. Northern Liang was the fief of a king with a different surname in the Liyang Dynasty. It was relatively independent, but it still belonged to the Liyang Dynasty in name. The Northern Mang was the enemy of the Liyang Dynasty and had been attacking the Northern Liang. According to the ending of << The Sword Snow Stride >>, the Northern Liang won and defeated the Northern Mang army.
Northern Liang had lost a large number of soldiers in the two Great Wars of Liangmang. In the first Great Battle of Liang Mang, the Northern Liang defeated the Northern Mang with an absolute disadvantage in numbers, but the price they paid was huge. It was reported that the border troops of the three states of Beiliang had lost more than 100,000 men, while the Northern Mang had lost 350,000 men. In the second Great Battle of Liangmang, there was no mention of the general losses. However, it could be seen that Beiliang had fought to the death in Youzhou, Liuzhou, Liangzhou and other places, and many soldiers had died in the battles. In short, the Northern Liang had paid a huge price in the two Great Wars of the Liang Mang, but they had successfully resisted the invasion of the Northern Mang.
Beiliang won in the end in the Sword Snow Stride ". Under Xu Fengnian's leadership, the Northern Liang had successfully defeated the Northern Mang army in two major battles. After Beiliang conquered Beimang and Nanchao, they confronted Zhao Family and finally took down Gu Jiantang, helping Zhao Family to obtain the ruling power of the world. Thus, Bei Liang won in the end.
The Northern Liang and the Northern Mang had fought two wars. In the first Great Battle of Liangmang, Northern Liang won. However, after the Second Battle of the Great Liang Mang, the Northern Liang army suffered heavy losses and was eventually defeated by the Northern Mang army.
In the end, Northern Wei was destroyed by Northern Zhou. In 557 AD, Yuwen Yong of the Northern Zhou Dynasty launched an attack on the Northern Wei Dynasty. After several years of fighting, the Northern Wei Dynasty was finally defeated. The last emperor of the Northern Wei Dynasty, Yuan Kuo, committed suicide.
Xu Xiao and the Northern Mang Empress were characters in Sword Snow Stride ", and there was a relationship between them. Xu Xiao and Northern Mang Empress had known each other when they were young. Empress Murong once had a good impression of Xu Xiao, but Xu Xiao did not reciprocate her feelings. Murong had turned back twice to wait for Xu Xiao to change his mind, but he left in disappointment. After Murong returned to the Northern Mang, she married the Northern Mang Emperor and gradually gained power, becoming the Northern Mang Empress. Before Xu Xiao died, the Northern Mang Empress came to see him. The two of them mocked each other, but they also revealed deep feelings and regrets. The Northern Mang Female Empress said that she had come south to see Xu Xiao while he was still alive. Xu Xiao and the Northern Mang Female Empress's fault and emotional entanglement became an important plot in the story.
The Northern Liang won the war of the Northern Liang and the Northern Mang in << Sword Snow Stride >>. Under Xu Fengnian's leadership, the Northern Liang had successfully defeated the Northern Mang army in two Great Battles of the Liang Mang. After Beiliang conquered Beimang and Nanchao, they confronted Zhao Family and finally took down Gu Jiantang, helping Zhao Family to obtain the ruling power of the world. Xu Fengnian chose to retire after the showdown with the Zhao Family, and Northern Liang also integrated into the Central Plains. With the support of Dong Zhuo and the Tuoba Family, Beimang retreated to the Norland and took a defensive stance against the Central Plains. Therefore, according to the information provided, the Northern Liang won the war between the Northern Liang and the Northern Mang.