If a Narcissist marries someone who refuses to indulge them will they get better?

My husband is a narcissist and has improved greatly in the past three years we've been together because I always fight him, never indulge his self-absorption and am unaffected by his verbal abuse. I am very successful in my career and attractive and nothing he can do or say has been able to shake my self-esteem which I think has affected his disorder by lessening his grandiose ideas of himself. He has told me that for the first time he believes he is with someone who is better than him! Now these days he is quite meek to me but the sadness remains in our relationship because his insecurity and self-hatred still manifests in his occasionally lashing out where he will call me names, etc. typical Narc stuff then end up apologizing. Like I said, I easily brush it off but am worried about his lashing out affects our child. Should I stick it out for a bit longer, perhaps he will change more or is there a plateau for a Narcissist's improvement?