What is a delinquent (offline) validator?
A delinquent validator is one that has stopped voting on new blocks (its main job) or has fallen too far behind the network to keep up. In plain terms, it's offline. While it stays offline, it earns no rewards, and neither do the people staked with it. Their SOL stays put, in their own stake accounts.
You lose rewards, not SOL, while it's offline
When a validator goes offline, your SOL doesn't disappear. It stays in your stake account, and there is no on-chain penalty that takes stake away today. What you lose is rewards: for as long as the validator is down, your stake earns nothing, and those missed rewards don't come back later.
A short outage costs little. The expensive kind is the one nobody notices, where a validator stays offline for days while its delegators assume all is well.
If your validator stays offline, you can move your stake. Deactivate it, wait until it's free, usually by the next epoch (an epoch lasts about a day) and sometimes longer when many stakers exit at once, then delegate it to another validator.
Flags, an uptime strip and alerts show when it's down
A validator that isn't voting right now gets a red Offline now flag, and its Score is cut by 60% at the next Score update.
Each validator page has a 90-day uptime strip that shows the days it was down, and a yellow Often offline flag marks validators that were offline on 5 or more of the last 90 days. Our Telegram alerts message you within minutes when your validator stops voting.
Questions
No. Your SOL stays in your own stake account, and no slashing (a penalty that cuts stake) has been switched on in Solana so far. You only miss rewards for the time the validator is down. If it stays offline, deactivate your stake and delegate it to another validator.