The bigger problem might be what it will cost to get things back where they need to be. Probably a lot more than $600k. How many of the knowledgeable developers are willing to come back to clean up the mess? Any of them? And at what salary? Possibly a lot more than they were paid before they were kicked out. If you can’t rehire the original developers then you might find others with the required technical skills - but probably not with the domain knowledge. And now costs and times increase further.
The bigger problem might be what it will cost to get things back where they need to be. Probably a lot more than $600k. How many of the knowledgeable developers are willing to come back to clean up the mess? Any of them? And at what salary? Possibly a lot more than they were paid before they were kicked out. If you can’t rehire the original developers then you might find others with the required technical skills - but probably not with the domain knowledge. And now costs and times increase further.