Android Alpha/Beta Testing group email requirement

So I am almost ready to launch my first app soon Yay! But before that we need to do some beta testing.

Now I really want to convince my company to use the google developers console to manage this. However they have raised some security concerns about being able to manage our who is in our beta group and who will have access to the beta if we don't do it internally. For instance if an employee quits/(is sacked) during beta he would still have access to the beta through his private gmail account.

So doing this through a google + community is out of the question. I want to know if I make a google group and invite the testers by using their company emails, will that prevent them from having access to future beta releases if they quit (since their email would be deactivated if they quit)?

Or would they need to create and link gmail accounts to the google group anyways to participate in beta which would mean that my company will not condone using the developers console for our internal beta?