Salesforce has the option to enable cascade deletion for lookup relationships. Thus, if you delete the parent in the lookup, the child will also be deleted. However, this option must be enabled on a per-organization basis. 

If I enable this option in an unmanaged package (so the option is enabled on that org), will the lookup still be cascade delete on any orgs that install the package (Even if that org has not specifically asked Salesforce to enable it)?

If not, what will happen? Will the lookup be converted to "clear field when parent object is deleted", or will an error occur when I attempt to install the package?