The COVID-19 pandemic has permanently altered workplace structures, normalizing remote work. However, critical evidence highlights challenges with fully remote arrangements, particularly for software teams. This study investigates employee resignation patterns at Ericsson, a global developer of software-intensive systems, before, during, and after the pandemic. Using HR data from 2016-2025 in Ericsson Sweden, we analyze how different work modalities (onsite, remote, and hybrid) influence employee retention. Our findings show a marked increase in resignations from summer 2021 to summer 2023, especially among employees with less than five years of tenure. Employees onboarded remotely during the pandemic were significantly more likely to resign within their first three years, even after returning to the office. Exit surveys suggest that remote onboarding may fail to establish the necessary organizational attachment, the feeling of belonging and long-term retention. By contrast, the company's eventual successful return to pre-pandemic retention rates illustrates the value of differentiated work policies and supports reconsidering selective return-to-office (RTO) mandates. Our study demonstrates the importance of employee integration practices in hybrid environments where the requirement for in-office presence for recent hires shall be accompanied by in-office presence from their team members and more senior staff whose mentoring and social interactions contribute to integration into the corporate work environment. We hope these actionable insights will inform HR leaders and policymakers in shaping post-pandemic work practices, demonstrating that carefully crafted hybrid models anchored in organizational attachment and mentorship can sustain retention in knowledge-intensive companies.