Sorry. But to find out an enemies HP and status, you'll need to cast Scan. Even if you've already done it once it the battle, you'll need to cast it again to see it again.

The menu option between Always and Once is refering to whether Scan will show it's full animation or a shortened one. When it's set to Once, the blue grid and detailed enemy bio will appear with one scan but anytime scan is cast again that battle, it'll be a simpler version. When it's set to Always, the blue grid + enemy bio appears every time. The only effect this has on the game is that it saves time for those critical timed fights such as Ifrit, the Black Widow, the Iron Clad etc.