In all seriousness, these are good points. I'm not a data center expert by any means, but here's what I know: The data center hardware has failsafes present by design, but they aren't disaster-proof being that they're in the same building.
To answer your questions: Yes, the backup storage box is in a separate chassis than the host machine that the Linode lives on; they have separate power supplies. The DCs themselves also have some sort of fire suppression. I don't know what would happen if there was an explosion.
Each data center has an internal private network with a pool of private IPs available for assignment. If a private IP is assigned to a server, it then has access to the private network.
Coming from a Linode employee, I can confirm this is true. Linode's backups live in the same data center as the server, but the systems are separated so that they don't directly affect one another.
Coming from a Linode employee, yes and no - you're not charged for uploading to an object storage bucket in general, but if you upload from a Linode over IPv4, that counts against your transfer quota for that Linode. Also, any outbound data (including to the same DC) is billable. It's also worth noting that any IPv6 uploads don't count against the quota. Here's Linode's pricing doc: https://www.linode.com/docs/platform/object-storage/pricing-...
To answer your questions: Yes, the backup storage box is in a separate chassis than the host machine that the Linode lives on; they have separate power supplies. The DCs themselves also have some sort of fire suppression. I don't know what would happen if there was an explosion.