Yes, no one said that you cannot keep using a release even after its EOL (End Of Life). Especially when you know that it works just find for your hardware, and the programs you use (and you do not plan to change hardware or use other programs). You can use it for as many years as you like.
The security issue is the most important factor in my opinion, as you will not be getting any security updates.
NOTE: I would like to make a correction to my above statement:
Zorin 6.4 will work till 4/2014, while Zorin 6.0 or 6.1 will work till 2017.
Zorin 6.4 will keep working even after 4/2014 as long as you update your kernel to the LTS one of 14.04.