Will my si joint ever heal 100%?

It certainly could. The si or sacro-iliac joint is the joint line where the two ilea and the sacrum come together to form the ring of the pelvis. If stressed this line of semi-fusion of the two bones can become sore and painful. This can be from an accident, over activity, or other stresses and inflammation. With the right therapy, rest, medicaiton and treatment, one may heal and never have another problem.
Sacroiliac joint. Need more details on injury to explain "heal".