While it is unlikely that a freestanding tub will tip over, it may shift position in time.
Although each freestanding bathtub has the potential to move somewhat, there are a few factors that reduce the likelihood of this happening.
In most cases, the weight of the water in the tub will prevent the tub from sliding, but some people choose to apply silicone sealant behind the leveling feet just in case. Because of this, the movement will be controlled. Maintenance might become somewhat more complicated.
Even freestanding tubs with antique pedestals and clawfoot bases are not at risk of toppling over, so no need for concern about this possibility.