> Recovering from scratch a whole infrastructure managed by many people over the years is a titanic task.

Half of the work is to know what you need, the other half is to know how you do it, while the third half is to cope with all the undocumented tinkering which happened along the way. So in that regard, starting from scratch can be acceptable, as long you are not starting from zero, and can build up on the knowledge and experience of the previous run(s). I mean, there is a whole gaming-genre about this, which is quite popular. And usually you have the benefit that you might be able to fix some fundamental failures which you had to ignore because nobody wanted to take the risk.