No, you don't lose your Monero if your machine restarts during syncing.
Discussion
it was a while ago. not even sure which computer I was using. tried several times to get back into the wallet. futile. it wasn't much at the time. probably a lot less now actually. not worth worrying about, but it does happen.
As long as you saved your seed words I don't know how this would be possible
i have them written down somewhere. I don't even remember what app I was using. computer restarted during a syncing and then I got login failures. couldn't get back in. I had mined a small amount, but it's gone. if it's recoverable, I'm not going to bother now. maybe if it takes off in my lifetime....