Since we can't know the intent, maybe leave it as `
` but add a `style="text-decoration: line-through;"`?

I didn't know W3Schools was so bad. It's really convenient to use (usually top hit on google, gives a short and easy-to-read description of the element and list of tags, old and new). Nothing against the other sites, it's just that W3Schools is usually the first hit on google :). I often check the spec directly as well, but it's not always enough. MDN looks like a good alternative. It suggests using a span with CSS instead of strike.