The project keeps moving on your own resources, not ours. From day one the code sits in an account of your own that holds it together with its full change history (the technical name: a repository), and the specification, the setup instructions and the task board live with you too. The other person already knows the project, because both of us work in the same code from the start, and every change is described in the list of changes, in your own language.
The contract has a handover clause: if we cannot continue, we hand over the full set of materials and every password within the deadline written into the contract, and you can pass the project to anyone you choose. Nothing in it exists only in our heads or only on our own computers.