When a node goes offline perminately, in order for your file shards/fragments to be repaired and stored on another node you need to run the client as a renter to check for missing file shards and repair missing file shards on the network.
I would like to purpose adding the ability for nodes (hosts) to do this functionality of repairing files for renters. This way renters do not need to run the client unless they want to upload files, download files, or renew their contracts.
If it will take lots of bandwidth or computing power for nodes to do this function, then I would suggest adding in the storage contracts an option for nodes to do file repairing for the renter for an additional cost.
To have nodes do file repairing, it will make sia feel like a true cloud storage system and will be robust for users who are digital nomad and for someone who has lost everything due to a fire, natural disaster, etc and cannot get a device or internet access for awhile but will be rest assured as long that they have their seed phrase that there files are safe, even when nodes go offline over time.
This is also essential for those who maybe cutoff the internet for months and therefore cannot run a client to ensure files are repaired if nodes are going offline, some countries due turn off the internet from time to time.