It would depend on the Queen and the hive, but generally an unsupported murder of another changeling, or consumption of a hive mate will result in banishment from the hive, and on some occasions even the plucking of the changeling’s wings.

A Queen will not kill one of her subjects unless enraged, as their echo would only remain in her hive mind and keep her from resting.

On their own and without a hive or steady supply of love, a changeling can rapidly lose themselves to their hunger.  After consuming all suitable foodstuffs from an area a hiveless changeling may very well turn feral and lose their mind completely, at which point they are generally hunted by any nearby sentients, or they starve to death.