Answer
The proposed decay conserves the spin angular momentum.
Work Step by Step
The $\Lambda^0$ spin angular momentum is $\frac{1}{2}$
The $p$ spin angular momentum is $\frac{1}{2}$
The $K^-$ spin angular momentum is $0$
The spin angular momentum on the left side of the decay is $\frac{1}{2}$
The net spin angular momentum on the right side of the decay is $\frac{1}{2}$
Therefore, the proposed decay conserves the spin angular momentum.
