Scramm was folded into other characters, with Stebbins getting his bad cold and Olson getting his wife, which the core group promises to care for if any of them win.

Scramm getting pneumonia was drawn out for quite a while in the book, but Stebbins having the cold was barely a single sentence in the movie dialog.

There were other instances where character traits in the book were melded into different characters in the movie, but that was to be expected. There's only so much you can do in a 90 minute movie.

Why do the walkers sign up for it? Some weird national pride. With the screwed up direction the country has taken in the story, entering the lottery for the possibility of representing your state in the walk is an honor of sorts.

!Is McVries dead? Yes, but not by the hands of the soldiers.
With him killing The Major, he might be viewed as a trigger that starts an uprising in the country, and if he is killed, he dies as a martyr to the cause.
I do think that he would soon likely commit suicide due to PTSD and extreme survivor's guilt!<.