If I understand correctly, you just want the scaling to stop when it gets too big and like hits a wall or some collider/rigidbody, but still be able to go back down

I think you could use OnCollisionEnter or OnTriggerEnter. Basically, when it collides with something, save the current scale vector3 and enable the stopscaling portion of script in the update function, thus making it so the scale is locked at that maxScale vector3. When it exits (not colliding), it will disable the stopscaling script and allow scaling to resume.

Here is an example with OnCollisionEnter:

    private var stopScale = false;
    private var maxScale : Vector3;

    function OnCollisionEnter(collision : Collision)
    {
       if(collision.gameObject.tag == "wall") //you don't need this conditional statement if you want it to stop scaling when it hits anything, this just allows you to be specific with what stops it's scale
       {
          maxScale = transform.lossyScale;
          stopScale = true;       
       }
    }

    function OnCollisionExit(collision : Collision)
    {
       stopScale = false;
    }

    function Update()
    {
       if(stopScale)
       {
           transform.lossyScale.x = Mathf.Clamp(transform.lossyScale.x, 0, maxScale.x);
           transform.lossyScale.y = Mathf.Clamp(transform.lossyScale.y, 0, maxScale.y);
           transform.lossyScale.z = Mathf.Clamp(transform.lossyScale.z, 0, maxScale.z);
    }

I haven't tested this script so there may be some bugs, but get back with me if it doesn't work. Good Luck.

If your collider is sphere or capsule there are methods to check intersection.

Physics.CheckCapsule
Physics.CheckSphere

methods does that.

Or, maybe you can make rigidbody of your objects kinematic and scale them up until OnCollisionEnter method is triggered.