I fail to see how sidecar applications improve resiliency. You are still dependent on these applications as they share the same lifecycle. They might fail to run, which means your main application won't run. It won't process those requests. So you still need your replication, circuit-breaker patterns, health checks and resource limitations to enable resiliency.

Sidecar helps reduce complexity in your code, introduce loose coupling and individual scalability. But it won't help with resiliency.