After Aslan left, Xi Wei started to analyze Zod's soul…More precisely, his soul was already destroyed through the torture of the Heaven-Cursed Body.
Perhaps Lord Hades that had control over the laws of death would be able to repair this soul, but Xi Wei had no way of doing so.
In conclusion, Xi Wei couldn't help but be curious about what the Heaven-Cursed Body exactly was.
Granted, Xi Wei had no intention of saving Zod in the first place.
Even though Xi Wei sympathized with him, but at the time his life was about to end, Zod was still a Tsujigiri that slaughtered many innocent lives.
What Xi Wei promised was only to pass down his skills and inheritance.
The way to do so, was of course to impart what Zod had learned over the course of his entire life to the players.