No one can answer this question. Maybe he can change a little. Maybe he can change a lot (although this is fairly rare.) Maybe he will not change at all. Maybe he will even get worse. There is no way to predict this.
Change is very, very hard for someone who abuses others, especially for someone who is older, and those with other serious problems like substance abuse or mental health issues. It is important for you to accept that you cannot change your abuser, as much as you might want to help him. He needs to seek out help himself if he wants to change. Your efforts will be ineffective because he does not believe that you know best. Sometimes backing off from an abuser helps him, because without his partner right there to control and focus on, he has the space to examine his own behavior and his need to change.
What if he wants to change?
For people who abuse their partners and admit that they are at fault, the best place they can go for help is a Batterer Intervention Program (BIP). There are many such programs available across the country. Learning takes place in a group setting, which has been proven to be much, much more effective than individual counseling or mental health services. To find the BIP programs near you, contact the DV Hotline or 1-800-799-SAFE.