I am a free game developer making my first indie game and I have encountered the policy that you can only earn <100,000$. So I thought that I would buy the pro version when it is about to hit 100,000$. Now I have a question that after pro expires and I earn 300,000$ do I get to keep it without any problems? If there are no problems with that then do I need to purchase pro again if it is going to hit 400,000$?,
You are ambitious not if but when you earn that much.
The license terms are pretty plainly written. If you (i.e. your company) are earning more than $100,000 in any 12 month period (regardless of how you made the money) you need to be on pro.