Alien certificate ans Dependant's pass (Nairobi)

Hi, I'm married to a Kenyan and I have a dependant's pass and alien certificate.
However, I've been out of the country for some time and I've noticed that my Alien certificate expires in July.

What happens if I wait until September/October, or later, to renew it?

And what about my dependant's Pass, does it expire? I don't seem to understand much from the stamps on my passport.

A friend of mine has told me that, if I don't renew these documents before they expire, I won't be able to apply for the permanent residence permit or for citizenship. Is that true?

I'd be really grateful if anybody could help.

Thank you very much!