Thanks to Xiao Ruiyuan's military achievements, his status in the army, and his connection with Chu Heng, the likelihood of being sentenced to death for defying the emperor's edict was slim. At most, he would be stripped of his official position and nobility.
Once Chu Heng ascended to power, there would still be a place for Xiao Ruiyuan to display his martial skills, so there was no need for excessive worry.
As for Mo Yan, she had too many concerns. If Emperor Huian decided to start with her, she couldn't defy the edict considering her concern for her relatives.