First things first - treating code as an absolute asset is a mistake. Same outcome may be produced by different codebase. Second - present team goes away after rewrite - it is what it is - code is derivative of a vision and team. Freeze of development of legacy is strongly recommended during rewrite. Now - rewrite: You slash an app into segments on principle of cause-and-effect - input data produces output data, which serves as input for next segment. Then if you are risk minimizer - start with tail of cause-effect chain, and rewrite this shit. Continue segment by segment. After each segment reflect on need to refactor new codebase.