Make out a list of what will have to happen for the project to have a reasonable chance to succeed. Firings, hirings, physical and virtual assets that need to be added. Any code or modules that need to be scrapped and redone from scratch. Lay out benchmarks and timelines that are realistic based on the needed changes. Take that to administration and see how much pushback you get. That should give you a good idea about how well it can work out for you.
Run, like the wind (scream “wildfire” too, if you can). This sounds like corporate disaster writ large. It’s nice to be wanted, but it really, really doesn’t sound like the company is behind this. The fact that you get to fill in for all the missing roles until they’re hired is another big, red, flashing sign that you’re screwed. There is absolutely no guarantee that those head counts will ever come along. Basically, you’re just signing up for being the fall guy, with a lot of stress and anxiety on the way.
If you think the title bump and salary raise would be helpful in your job hunt, by all means take them and keep looking. If not, then don’t take them, and keep looking.
If this were me, and I had another option, you would not see my ass for dust.
The company wants to do anything they can to retain you, except change. You are now doing the work of three managers, and the company wants to make it official.