If the value you're looking for is just 0 downtime, then k8s solves that for you. As others have pointed out, the BEAM/Elixir/Erlang give you great process isolation and resilience to small failures, timeouts, weird transient issues, big short lived spikes traffic, and stuff like that.
With respect to user data, a supervised process can crash and the supervisor can restart with the last known good state of that data. It requires some thought on the part of the developer to achieve this, but it's really powerful.
I guess i'll have to try OTP one time to understand why so many people rave about it. I only know one guy who had made real work with erlang / otp and he told me it was beautiful, but not quite as relevant anymore, because of k8s. But i guess i need to make my own opinion.