Will HIIT boost my cardio over all enough to let me keep going

I'd like to know as well

Up to a point.
Then it will plateau and not move beyond that.
But there's something you should know.

There is a 100% chance that you are not doing HIIT and an even greater chance that if you do correct hiit then you will seriously hurt yourself.

If you want to increase your "cardio" for whatever reason that is...
I suggest interval training rather then HIIT.

Interval training is doing your basic cardio routine but occasionally pushing yourself a bit harder then normal then after a bit going back to your regular pace.

A good example is if you jog at a good slow pace for thirty minutes, but speeding up the pace till you're running a bit faster then slowing down into your jogging pace.
Continue doing it like that for the entire run.

And by speeding up I don't mean sprinting at fullspeed to hell with your joints and heart health. I mean run a bit faster.