"An ounce of prevention is worth a pound of cure." The two biggest categories of reasons why missionaries come home permanently from the field (attrition) due to preventable reasons are unrealistic expectations and lack of relational accountability. The sending church can be the solution for each of those. Rethink the candidate's pre-field training and qualifications. Build a strong web of relational accountability from the very beginning. Send and shepherd them well for long-term faithfulness and effectiveness.