To evaluate participants with follow up interviews, who completed residential rehabilitation and now currently in the community. The objective is to assess why they relapsed if they did, and what helped them to be abstinent after engaging with a community.
This does not necessarily require a "tool" but rather a strategy of questions to address the focus of the investigation.
If your focus is on treatment improvement, you would need to be on the value of treatment components in achieving remission. For example upon follow-up after treatment, we asked thousands of individuals how helpful components of the treatment were. Importantly, this consisted of the question of how helpful the components were for achieving recovery - not how "satisfied" they were with the component. What we found was that informal time to interact with other patients was one of the components rated as very important. Wa found that if group therapy and readiness to engage with peer-support after treatment also were highly related to continuing remission.
If your focus is on factors in the community that contributed to continued remission or relapse, then you would need to have questions about such factors, such as having a sponsor, attendance at peer-support meetings, having friends and/or relatives who are either supportive of detrimental to sustaining remission, etc. Such questions could also focus on cultural norms, environmental factors, such as prevalence of stores selling alcohol or drug dealing, etc., living arrangements (presence of recovering or using individuals), and work environment.
I agree with Norman G Hoffmann, and would suggest that your read the following paper based on a qualitative study in a Norwegian sample to get some ideas when planning the study:
Pettersen H et al (2019) Helpful Ingredients in the Treatment of Long-Term Substance Use Disorders: A Collaborative Narrative Study Substance Abuse: Research and Treatment 13:117822181984499
DOI:10.1177/1178221819844996
You basically don't need a tool for the interviews. As per your objective, you need to develop an interview guide (a set of questions) that will assist the interviewer during the interviews and will help you get specific answers.
The questions must be open-ended and should be developed using previous literature.
A qualitative paradigm will be most suitable for your study objective.
I agree with the first paragraph of Ammar Suhail's response, but whether or not to use open-ended or fixed-options questions depends on the level of clarity concerning outcomes. If there is no or little prior knowledge or theory, open-ended questions are likely to be good, but analyses could be more problematic. On the other hand, if one has specific theoretical foundation questions with ratings or yes-no might be preferable and easier to incorporate into quantitative analyses.
Norman G Hoffmann Thank you for adding more details, I certainly agree the choice of method collection will depend on the research problem/question. I hope our answers help Lahiru Channaka