There are 3 modes of decay via which a $$\Omega ^{-}$$ particle can decay

This is one of the decay:

$$\Omega ^{-} \rightarrow \Xi ^{0} + \pi^{-}$$

Baryon number is conserved. Strangeness number is not conserved so that would imply that the interaction involved is weak Apparently, the rest mass isn't conserved either.

$$\Omega ^{-} = 1672\frac{MeV}{c^{2}}$$ $$\Xi ^{0} = 1315\frac{MeV}{c^{2}}$$ $$\pi^{-} = -140\frac{MeV}{c^{2}}$$

Really, what does this mean? How is this a possible decay mode if the rest mass isn't conserved?