What happens if I've failed to respond to naltrexone?

For alcohol? First, no medication by itself will cure the problem, other support is needed, meetings, counseling. Genetics seems to play a role in what meds are most helpful for certain individuals. There are other meds that are helpful for treating alcohol dependence such as topiramate, campral, ondansetron, Gabapentin and Baclofen are some other meds that may be helpful.
Tell me more. naltrexone blocks opioid receptors. I am not sure what you mean by failing. Most likely, the receptors were blocked. Perhaps you say that this blockage did not give you the results you expected? Then add more to your treatment. If you are taking Vivitrol and you relapsed, I sometimes see that first few shots do not work as long as expected. Schedule your second shot approximately three weeks from.
Modify Treatment. Consult with your pain specialist in this situation. Never self adjust medication use without expert guidance. If you "failed" treatment your physician may consider adjusting your dose or switching you to another medication. Again, never self adjust any medications, especially in this class of drug as it can result in serious consequences. Addiction and pain management specialists are best.