Objectives Little is known about the experience of family caregivers of patients who require prolonged mechanical ventilation (PMV). We examined the perspectives of caregivers of patients who died after PMV to explore the role of palliative care and the quality of dying and death (QODD) in patients and understand the psychological symptoms of these caregivers. Methods A longitudinal study was performed in five hospitals in Taipei, Taiwan. Routine palliative care family conferences and optional consultation with a palliative care specialist were provided, and family caregivers were asked to complete surveys. Results In total, 136 family caregivers of 136 patients receiving PMV were recruited and underwent face-to-face baseline interviews in 2016-2017. By 2018, 61 (45%) of 136 patients had died. We successfully interviewed 30 caregivers of patients' death to collect information on the QODD of patients and administer the Impact of Event Scale (IES), Hospital Anxiety and Depression Scale (HADS) and Center for Epidemiologic Studies Depression (CES-D) scale to caregivers. We observed that more frequent palliative care family conferences were associated with poorer QODD in patients (coefficients: -44.04% and 95% CIs -75.65 to -12.44), and more psychological symptoms among caregivers (coefficient: 9.77% and 95% CI 1.63 to 17.90 on CES-D and coefficient: 7.67% and 95% CI 0.78 to 14.55 on HADS). A higher caregiver burden at baseline correlated with lower psychological symptoms (coefficient: -0.35% and 95% CI -0.58 to -0.11 on IES and coefficient: -0.22% and 95% CI -0.40 to -0.05 on CES-D) among caregivers following the patients' death. Caregivers' who accepted the concept of palliative care had fewer psychological symptoms after patients' death (coefficient: -3.29% and 95% CI -6.32 to -0.25 on IES and coefficient: -3.22% and 95% CI -5.24 to -1.20 on CES-D). Conclusions Palliative care conferences were more common among family members with increased distress. Higher caregiver burden and caregiver acceptance of palliative care at baseline both predicted lower levels of caregiver distress after death.