Yes, you can still use Azure AD. When you use Office 365 that means you are creating users in Azure AD. You can able to login to https://aad.portal.azure.com and can see all your identities there.
Although you are not continuing with Office 365 business essentials (sad to hear it) still your identities are in the cloud with Azure AD. You can use Azure AD FREE features like single sign on, user provisioning and connect all your apps from Azure AD.
Note that you will not be getting any bill if you dont use the premium services like MFA. If you plan to use our premium features like Conditional Access Policy, Governance etc then you can buy Azure AD Premium as needed.