There are two key elements in Germann's argument:The concept of "satta" in the Theravadin Abhidhamma is the concept of not-existent (satta-pannatti is the avijjamana-pannatti). There was no one who could select events. This means that in the beginningless Buddhist past (the chain of conditioned dhammas does not have a first link) all possible events would have happened. If the realization of Nibbana refers to possible events, then all the causes and conditions of the impersonal-mechanical achievement of Nibbana should have formed in the past.
(1) Whether there exists of an ability to select event. That ability must be outside the beginningless chain of conditioned dhammas.
(2) Whether the realization of NIbbana refers to possible events.
Implication of (1):
If you hold the belief of beginningless chain of conditioned dhammas, then any ability to select an event must necessarily be an emergent phenomenon of the begninningless chain of conditioned dhammas. This means that any self with an ability to make choices must be an emergent phenomenon of the beginningless chain of conditioned dhammas. Taken to its logical conclusion, the tenet of cessation would lead to a tenet of annihilation. Such a tenet would be the same as the tenet of non-existent of satta.
Implication of (2):
Assume that the realization of Nibbana refers to possible events.
Assume also that all possible events can only exist within the beginningless chain of conditioned dhammas.
If we divide the chain of conditioned dhammas into a portion that is beginningless until now and a portion that is from now to the some future point in time, then the first portion is must be infinite, since it is beginningless. If it is infinite, then Nibbana as an event must be somewhere in that portion.