User is able to create a Flow in a deleted environment

Don't think there is a recycle bin for Flow environments, at least not that I know of. The only 2 places where I can see environments is in the top right corner at flow.microsoft.com (clicking on your username allows you to select the environment where you want to create a Flow) and at admin.flow.microsoft.com. 

This trick allows users to create an environment for Flows which is hidden from the tenant/Flow admin. Don't think this will happen accidentally as the second user has to create a Flow in the environment while it is being deleted by the user that created the environment. The only way to delete the environment now is by reaching out to Microsoft support as nobody can see the environment at admin.flow.microsoft.com.