I think what you are asking me is “If I download a game with Extra and then drop back down to Essential, will I still have access to those games?”
The answer is no. You lose access, just like you lose access to the free monthly PS Plus games when your subscription runs out.
You can however do game share with someone who you trust to login with your account and you theirs. This means you could split the cost of a membership 50/50 if you have a friend willing to do it.