What would happen to you if you were a Christian and then you left the church but still believed in God?
Salvation is not dependent on going to a particular church or being a part of a particular denomination. It is solely dependent on acknowledging that you are a sinner, accepting Jesus Christ as your personal Savior, believing that He died on the cross for your sins and rose again, and repenting of your previous sinful activities as the Holy Spirit illuminates the things you need to change.
See The Gospel's Message for scriptures about this process and how to go about accepting Christ as your Savior.
Having said that, you also need to understand that Satan is attacking everyone that he can, Christian and non-Christian alike. He attacks Christians because he hates us and what we stand for. He attacks non-Christians because anybody he can take before they accept Christ as Savior is a win for him. So you will be under attack regardless of whether you attend church or not.
The New Testament warns to not forsake assembling yourselves together as you see the time approaching because the writers knew that then, like now, we would need each other's strength to stand firm to the end (Heb. 10:24-25).