I'm not really sure what a 'Plan B' might entail, other than trying to get re-booked on another (later) flight after you miss your original one. But that goes without saying, and can be a major hassle, not to mention potential additional expense.
Not much of a Plan B IMHO.. The alternative is to book a later outbound flight in the first place, which allows ample time to make the flight, and considerably reduces the need to even have a so-called Plan B.