Re: Go ahead
Is Ksplice the default? No, it isn't. It *can* be used, and you have to test carefully it won't create more problems than it solves.
Sure, you're not required to reboot - but until you do, the old kernel is active and any vulnerability in it also. It's a matter of managing risks.
Nor Windows Server reboots on its own unless you configure it to do so.