I thought the ending was actually quite good, very sad really. The one illogical seeming part was I wondered why Randall didn't jump through the hole to get to the boat as well but then I was reminded of the fact that he couldn't swim!
The ending would have been great in my opinion if he drops all his things and then tries to swim. I'm sure that swimming must be easier than taking on a big group of zombies. It just felt illogical. It could have been so great!