I think he's 99.9% sure Shen Wei is dead and gone. But maybe there's a 0.1% of hope that he can't quite give up on? The faintest of chances that this is a strategy by Shen Wei that gets them both out alive somehow (like they have every other time). It's a tiny spark that I think is only extinguished when Lin Jing comes back and Shen Wei doesn't. Idk.

Huh. I think he's 100% sure Shen Wei is dead and gone, but when Lin Jing comes back, that certainty is suddenly gone and hope sparks - only to immediately be snuffed out again. :(