The penalty for missing attestations is exactly the same as the reward for a successful one. Any downtime penalty will be recovered in the same amount of uptime.
Proposing a block is rare. Depending on the size of the validator pool, a single validator will on average only propose a block every few months. If you are unlucky enough to be offline at the time that your validator is asked to propose a block, that's also ok.
The Ethereum network is robust and designed to handle these situations. If you miss your block proposal, the slot that should have contained your block will be empty. Other than the lost rewards from missing the block proposal, there are no penalties or slashing that occurs from a missed block proposal.
Automated failover and backup systems may seem like a good idea, but they are much much more likely to cause a slashing event (e.g. double proposal) than a manual recovery process. Missing out on a few days of rewards may seem bad at the time, but getting slashed and potentially missing MONTHS of rewards is a lot worse!
- TODO
- Initial trouble shooting
- Resyncing