Like on the default XP bar there's an arrow that shows the exact point when your vitality would run out. It's usually pointing to the right because it extends beyond your current level, but when your vitality gets low enough, the arrow points to the point in the orange bar where your vitality would run out, or if you're in the same orange bar, a blue arrow at the bottom would then point out a more detailed place where your vitality would run out. (Edit: I don't know if there's a numeric value associated with that or not, or if it's just a feature of the default xp bar.)
It's nothing serious; as I said, you have double vitality until your vitality is zero percent, but if it's something that can be done, that might be nice. Not a big deal, though.
And yes please, putting a tooltip on the little XP main display would work, as I kinda like being able to switch the top bar on mouseover
