The last episode is called "No Time Left". From this and the ending of episode 4 we assume that means there is no time left for Lee. However what if there is actually no time left for everyone. Think about it. Up until now you have had the choice to kill off almost every character the ones you save die eventually anyway because it is The Walking Dead. Not a Disney story. If you think they are going to make it back to the boat and it hasn't been stolen/over run by walkers/already sailed out on it's own then I think you will be in for a shock. Think about this:
-Lee saves Clem but Christa and/or Omid dies.
-Kenny loses it with Ben and kills him
-Kenny, Clem and Lee get back to the boat and are being followed by an enormous amount of zombies. However, the boat is already halfway out to sea and it's Vernon and his group on the boat.
-Cue dramatic scene where the three of you die
THE WALKING DEAD.
Or something along those lines...