[@Zyx]
The gods are essentially forces of nature, with their respective characters embodied in the laws of nature. As such, I'm not sure whether ascension to godhood proper is possible in this universe's lore. There's certainly no precedent for it.

Oh, and there's one limit to magic I forgot to talk about: Authority. While I don't want to bog it down too much in numbers and rules, as a rule of thumb, demigods have enough magical authority (think mana) to do something that'll slightly affect the whole world. When divided up between their contractors, it's usually sufficient to do something flashy and overpowering once per encounter. It's strong, but you won't be burning holes to the planet's core without incurring backlash.