[TikiTDO]

That really depends on quite a few other factors: how big is the team? What development methodology do they use? Does the leadership understand how to manage and direct a rewrite? Are there people that understand the full scale and scope of the system? Does the system interact with legacy components that can't be modified? Are there political factors in play? These are just a few of the questions that can change the outcome of any given rewrite.

You mentioned hidden bugs, but what about hidden "features" that may be a critical part of existing business processes for core parts of the company? Developers really like to believe they are at the center of the wheel due to the complex work they do, but a lot of the time they are not the ones that actually create the cash-flow.

I've been part of rewrites that have succeeded tremendously, but I've also been privy to utter failures that have cost millions, and led to entire teams getting sacked.