A coworker really wanted to be a technical lead on a firmware project so our boss gave him one. Part way through our boss asked me to help the coworker out but

A coworker really wanted to be a technical lead on a firmware project so our boss gave him one. Part way through our boss asked me to help the coworker out but I had a tough time understanding his code. Soon enough he admits that his is leaving the company. He created too much of a mess and wanted to bail out. Suddenly it was all my responsibility. And this was with an major customer we had multiple partnerships with. So somehow I had to salvage everything without making them aware the mess we were in. So over the next 3 months we would give them weekly engineering builds while totally rewriting the code piece by piece. Once we were back on track it was much smoother. It helped that our management didn't micromanage me and the customer engineers were brilliant and a breeze to work with. It was all about the code, requirements and doing the right things. Our progress meetings were literally 15 minutes week. Everything else was technical discussions and development.