The solution I use is to have all Jenkins config and pipelines in DSL (CasC does it for Jenkins, plus seed jobs, plus Groovy pipelines.) Once you have that, it becomes trivial to bring up an additional instance of Jenkins that looks exactly like your current one. You can check your pipelines there for a while, or rsync the build history and switch over to a new instance with a DNS update. Once you reach this point, it ceases to matter how many instances you have, you can have as many or as little as you want.