Lü Wende survives - Fate of Song?

Lü Wende was a Chinese general during the 1200s, one of the only to defeat Mongol forces in battle. He was reportedly planning an attack to dislodge the Mongols from Xiangyang when he died in 1270. He was replaced by his less influential brother and the Mongols ultimately took over the Song.

What if Wende survived? How would they do against the Mongols around Xiangyang? Or were the Song already doomed to lose by this point?
 
The Song were already doomed to lose by this point because of improving Mongolian military tactics in the 1270s over the 1260s.
 
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