I would pass on the job. It sounds like a mess. Taking over someone else's projects most likely never turn out anything less than a nightmare.
The facts in which the other contractor was released puts zero confidence into anything they did was properly done.
My bid would include tear-out of anything the previous loser did, and the start of a new project with all of your own materials. The homeowner can get the existing material off-site or tell the other contractor to get their crap outta there.
There is no way you can provide any type of warranty unless you excavate to soil and start over, and if the customer agrees to not having a warranty, you have put yourself in a bad position if something does fail. More than likely the full story would never surface and YOU would be the one blamed for shoddy work.
There must be some other jobs you could be doing instead.