I'm not the person you're responding to, but I believe I can answer that question as well.

Dokku essentially just started a container. If your server goes down, so did this container because it's just a single process, basically.

Other PaaS providers usually combine it with some sort of clustering like k3s or docker-swarm, this provides them with fail over and scaling capabilities (which dokku historically lacked). Haven't tried this k3s integration either myself, so can't talk about how it is nowadays.