According to our current understanding of physics based on the theory of relativity, it is not possible for an object with mass to travel faster than the speed of light in any medium or in empty space. The theory of relativity sets a universal speed limit of c, the speed of light in a vacuum, as the maximum attainable speed for any object with mass.
If we consider a hypothetical scenario where an object were somehow traveling faster than the speed of light in a medium and then released into empty space, our current understanding would suggest that the object cannot maintain that speed. It is not a matter of slowing down; rather, it is simply not physically possible for an object with mass to exceed or even reach the speed of light.
According to special relativity, as an object with mass accelerates towards the speed of light, its energy and momentum increase significantly, approaching infinity as it approaches the speed of light. As a result, the energy required to accelerate the object further increases infinitely, making it impossible to reach or exceed the speed of light.
Therefore, it is widely accepted in modern physics that objects with mass cannot travel faster than the speed of light, regardless of the medium or the subsequent conditions in which they find themselves.