We wan't to use Nintex in SharePoint online but has a question about backup/recovery in 365. If a sitecollection/sub site is getting restored from Microsoft support how is recovery of workflows handled in Nintex 365. Is this possible or is history lost for workflows and Items?
Workflows are provisioned to a particular object (site/ list/ library) thus when restoring a site with its contents workflows should be restored as well. However the "Designer" is not present on your tenant, but is a service delivered by Nintex. So although you should have currently published workflows in place, to edit them/ overwrite you still need to use .
Workflows history and tasks is again kept within your tenant content database so if Microsoft recovers your SC or subsite successfully, all data should be recovered as well (list/ library items, attached workflows, etc..)
However the most protective approach is to handle backup of your workflows by your own - whenever you create and publish a new version of the workflow export it and store in a safe place, so if you need to recover it, just import the workflow.