What happens when a user have more than 10 planets and you destroy his base (Hp) what is going to happen to his colonies??, will they will be destroyed too or what??

You cannot destroy planets but you can abandon them.
I dunno what happens if you abandon your home planet though. I never tried,

Another question.
How long will the destroyed planet (name) last?

You can't abandon you're homeworld. As for the time limit on destroyed planets, i think Slash said somewhere it's 48 hours? I'm not quite sure though.

-Istalris-

Correct. Typically, destroyed planet status lasts 48 hours.

You can created new colonies as soon as the the planet is abandoned.