Back in April i had 0 demerit points, then in that month i got busted a few times and ended up with about 18 demerit points =)
I didn't lose my license at that time because i hadn't paid all the fines, etc etc. I then got caught AGAIN 2 months later (still hadn't paid 2 fines) and lost a further 3 imaginary points (grand total of 21 demerit points =)). The copper gave me my license back, told me to pay my outstanding fines, and enjoy public transport.
Once I paid all my fines, I got a letter in the mail a month later (total of about 4months from the time i went over the 12points) stating when I will lose my license and for how long (in my case a total of 6 months (3 months for losing 12pts, and 3 months for getting busted doing 30 over)).
It's been over 4 months now since I lost my license, and I tells ya, it's a kunt.
If this is the first time you've lost your license, you also get a choice to take "1yr on 2points" instead of losing it for 6 months meaning if you get busted just ONCE, you lose your license for double your original suspension duration automatically.
Summary: You can legally drive until you get that letter. Once you get your license back, you will get all your points back unless it states otherwise in the letter. Try not to drive when you lose it or you will get "pwned". =)