Is it possible for an employee to be fired for bad mouthing or gossiping a manager who was recently terminated?

Our manager was recently terminated and several employees in our department cannot stop gossiping about the situation and are bad mouthing the manager. Human resources is currently investigating the issue. Is this grounds for immediate termination or just a simple 'write-up'?
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Depends on what the employees were saying. If what they were discussing was supposed to be confidential, they might get a warning.

If people got fired for bad-mouthing employees (or ex-employees), most offices would be empty.
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No employees can be terminated if they continue to talk and gossip about the manager with the fact that might be the cause of the termination. Rumors are not only hurtful, but they are inappropriate for the workplace.
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yes its bad
It looks bad for the company you are working for.