Though we love collaborations, we are aware that there might be times when it just doesn't work out.
In order to remove a collaborator from your project, from your profile page, open the ellipses menu and click "Collaborators" (1). Click "Remove" next to the collaborator(s) you wish to remove (2).
There are also a couple of things you could do before you start a collaboration in order to feel more safe about your project.
Make a copy of your project by going into the File menu in the studio and choosing "Save as..."
If you are a Premium user, you can use Time restore to open up a previous version of your project and create a backup even after you've started a collab.
If you change the name in the studio, the next time you save it you will be asked if you want to "Save as new".
(1) Profile page - ellipsis menu - Collaborators
(2) Profile page - Collaborators
(3) Collaborators dialog