Sorry to hear about your injury. The ACL has no blood supply, so it can't heal on its own - once it's torn, it's gone.
To answer your second question, it really depends. The ACL provides lateral support for the knee, so without one the risk is that under lateral pressure the shinbone will move too far in relation to the thighbone. This puts other structures in your knee at risk of damage, especially the meniscus. Living without an ACL also leaves you at risk of osteoarthritis in the long term.
Having said that, roughly a third of people are able to cope without an ACL without any major physical restrictions. (A third are able to live without it but have to give up most sports, and a third have a knee so unstable that even everyday activities cause instability and buckling. If you're going to try and live without the ACL for a while, the most important thing is that you start seeing a physiotherapist and start a muscle strengthening program. This will provide extra support and stability for the knee. However, you should also talk to your Ortho about whether it's advisable to continue playing football without an ACL. Football involves cutting, pivoting and contact, and is one of the highest risk sports for the ACL - it generally wouldn't be considered a good idea to go on playing without an ACL unless your leg is exceptionally stable.
Having said this, of course every case is different and you should do some research into the risks of ACL deficiency before making up your mind. Do talk to your surgeon, too; having tested your leg he will be able to tell you how much laxity there is in the joint. Unfortunately from your description (the knee never feeling quite right after the injury, and the regular discomfort you're experiencing) it doesn't sound as though your knee is 100% stable, which means that you do need to be careful and check with your doctor about the activities you should be doing. Pain is a sign that the knee isn't happy, so it's best to pay attention to it.
Good luck! I hope that the MRI shows something else is up rather than the ACL - it's definitely a tough injury to deal with, and it's hard making the decisions around surgery when you have an active lifestyle.