I have been involved in a successful rewrite. It cost billions of dollars and many years when the code wasn't working so the old system was still in use. We also ended up bringing over some old code directly just to get something - anything - functional at all. For many years my boss kept the old version running on his desk because when there was a question that old system was the requirements.

Today we only have to maintain the new system (the old is no longer sold/supported), and the code is a lot better than the old one. However I suspect we could have refactored the old system in place for less time/money and been shipping all the time. Now we have a new system and it works great - but we already have had to do significant refactors because some new requirement came along that didn't fit our nice architecture.