>to last minute catastrophic product failures
You have to have a product that works. People are trusting part of their business to your software. Depending on your software, they also have to spend a lot of time and money with integrations, training and all that. It's a large commitment that isn't easy to reverse.
If your software was working perfectly and provided obvious, quantifiable value, do you think you would have reeled in those clients? If so, slow down the features and concentrate on stabilizing the software. To do this effectively you need to have both an eagle-eye QA person/team and an existing beta client. The more beta clients the better, because people will use (and break) your stuff in ways no one in your company imagined. While you are doing this, make sure the people who are demoing it know a happy path and are disciplined enough to stick to that and can explain away the problems. For them to be able to do that, you have to have a committed relationship with them, especially before demos. You also need to be in constant communication with your clients and make sure they know you are turning things around. You need to show them proof with quick releases on the most painful items and constant improvement. Proper triage is big in the beginning and majority of this phase.
You also might want to ask your investors who are bullish on the product if any of their other investment companies or connections have any need for your software. They usually have connections that you and I probably wouldn't.
That's the best advice I can give given my experience. There is a lot more in the details but that's the top points. I've been the head technical person in 2 turnarounds now, but they had existing (but angry and fleeing) clients. We had the software stabilized within a year, but it's a grueling process. Expect nights and weekends for the first 3-6 months, depending on where you are, then things will go more smoothly.