I know that I can buy property in the US while I'm holding G4 visa.
However, I'm not sure what will happen to the property if I don't carry the G4 visa any longer, i.e. if I leave my employer:

Will I lose the property?

Can I keep it? For how long?

Will the capital gain tax be different from the time I had the G4?

Thanks

In US, aliens can buy properties, so it has nothing to do with your visa status. You can keep it as long as you wish. A large percent of million dollars homes in US belong to foreigners who are not permanent residents/US citizens.

Don't jump to capital gain tax that fast, you will have to pay property tax each year, and number could vary depending on its value.