in the unlikely event (that) (something) happens
If a very improbable outcome turns out to be the case. I wouldn't worry too much, but in the unlikely event that you lose your job, you can always come live with us for a while. In the unlikely event I win the lottery, the first thing I would do is travel to Jamaica.
in the unlikely event
If something improbable should occur. For example, In the unlikely event that I'm held up, please cover for me, or In the unlikely event that we should have snow in May, we're still well equipped to cope with it . Also see under in case, def. 2.