If you see your ex-colleague(s) outside of work after you left the organization, will you still greet him/her for a conversation or intentionally avoid him/her?

Will give a hi and bye lar. Singapore is so small, you never know when you will meet them in the same company again

I would greet if I see them/ eye contact.. If not, I might just pretend I didnt notice them.

Depends

If i'm still in the industry, i wouldn't burn bridges. A simple nod and smile would suffice and wouldn't hurt - if we do actually bump into each other that is :)