It doesn't have to be impossible to get back to skiing after an ACL injury. However, it does require specific, goal oriented training ( and preferably a good surgeon). I can help you with advice on the first part.  In the following you can read a little about the principles.

Usually when an ACL is torn it means your balance on that leg gets poorer.  That's because the ACL contains little receptors that tell you what position your knee is in and what you need to do to correct for balance.  The connection to these receptors are broken when the ACL is torn, so you need a lot of balance training, or proprioceptive training to get good balance reflexes again.

It is also very important to strengthen the hamstring muscles.  They assist the ACL in holding the tibia under the femur, thus stabilizing anteriorly.  If, for instance, you get in the back seat while skiing and you want to pull yourself up, then you would contract your quadriceps muscles to avoid bending your knees further and you hip extensors (hamstrings and glutes) to move the hips forward again.  If your hamstrings are strong and used to cocontracting, then they will help decreasing the load on the ACL in this case.  If they are weak, they will not contribute as much and the ACL will be under relatively more stress.

If your ACL is partle or completely torn and you didn't have an ACL reconstruction then obviously, the hamstring strength becomes even more important.  Otherwise you knee will be very unstable and you run a great risk of doing even more damage to your knee.

Strength training should preferably be performed with one legged exercises, because it is very easy to compensate unconsciously.  Most people don't even notice, bu the problem is that your strong leg then will get stronger and stronger and your weak leg will get weaker and weaker.  Another problem is that these imbalances might soon shift to other parts of the body causing other injuries.

YoFinally, you need to train the agility of your legs.  The communication path to your leg muscles will most likely have gotten a little rusty after your injury and you might not find it all that easy to make quick shifts in direction or absorbing a shock or a landing.  Through agility training you can get those inhibited movement patterns back
You might have to start by simply sitting on a chair, tapping your foot as fast as possible and making small patterns with your foot such as triangles and squares with fast, ittle movements.