H1B status expiring

If the h1b extension has been filed, but the case is still pending and the original h1b visa expires before the renewal comes, does the visa holder need to leave the US or can they continue to work in the US

If the h1b extension has been filed, but the case is still pending and the original h1b visa expires before the renewal comes, does the visa holder need to leave the US or can they continue to work in the US

If your extension was filed before the expiration of your H-1B you're OK.

how long would status be ok for

Your H-1B extension is pending. You're OK until INS approves/denies the H-1B extension.

Just make sure you don't leave the country while your case is pending