I've accidentally deleted a role, can I create a new role with the same name?

No, there couldn't be two roles with the same name, whether they exist at the same time or one is already deleted. The only way to re-add a deleted role is to add some variation to the role name. You can add a prefix or suffix to the role, as long as it's not exactly the same. For example, if you deleted a "Consultant" role, you can re-add it as "Consultant I", "I Consultant", or some other variation.