If you get it as a child, you will most likely end up with a lower IQ, though, which certainly is a lifetime affliction.
How much malaria costs when it is dormant is something I don't know. My intuition is that there is a cost (for example in a heightened inflammation response which is hard on the body) but I simply don't know.
You can get re-infected. As far as I know, it doesn't stay dormant in your body (like say Herpes). But I'm not a doctor, just had it a few mild times as a kid.