I agree that it's unreasonable to expect that Quirrell could have anticipated the entire chain of events that led to the duel with Bahry. However, it's not at all unreasonable to expect that a duel with one or more aurors would occur at some point during the course of breaking in and out of Azkaban, and in fact we know that Quirrell planned for this contingency, because he gave Harry standing orders for what to do if/when it happened. So, while that fight was not inevitable, a fight was always likely.