Yes, should there be a critical need, Rancher can provide patch fixes to address issues root-caused in RKE-provisioned Kubernetes clusters. As a first option, Rancher will investigate if the fix is already available in a later version of Kubernetes. If it is, Rancher will provide a newer version of its product that is validated and certified to work with the later Kubernetes version that has the fix. Or validate and certify one of its existing versions to work with the later Kubernetes version that has the fix.
Further, Rancher can submit a PR for the fix to Kubernetes for consideration to be accepted into upstream. However, there is no guarantee that the PR will be accepted and merged into upstream Kubernetes.