Does this reduction mechanism of an diazonium via stannic chloride sense?
Agreeing with Jan's comment, there are a few problems, and they all have to do with your reducing agent. That's not tin!

Tin is $\ce{Sn}$ and not $\ce{Zn}$ (zinc). Your mechanism is using $\ce{ZnCl2}$, zinc chloride. Let's say you made a typo and replaced $\ce{Sn}$ with $\ce{Zn}$. Your electron configurations match tin and not zinc. Then your mechanism is good. $\ce{SnCl2}$ is a reducing agent and could do this reaction. $\ce{SnCl2}$ is not stannic chloride, but stannous chloride. Stannic chloride is $\ce{SnCl4}$. Regardless $\ce{SnCl2}$ would work. $\ce{ZnCl2}$ would not work. The zinc in $\ce{ZnCl2}$ is already in zinc's highest common oxidation state. $\ce{ZnCl4}$ does not exist.