Depends on a lot of things. If the 0day is an RCE they would need another privilege escalation exploit. How easy that would be depends a lot on how your system is setup.
But the short answer is probably not. Unless you are running Qubes or something, if someone can exploit an RCE then they can probably own your system.
But the short answer is probably not. Unless you are running Qubes or something, if someone can exploit an RCE then they can probably own your system.