warning don't read the following if you have not beat the main story atleast once cause there are spoilers.
the reason why Roland had to die is cause the voice actor that does his voice doesn't want to do voice acting anymore. as to why blood wing had to die gearbox software knows why. when the grim reaper pulls your number there is no way out 16:36, March 23, 2014 (UTC)
This is the answer for bloodwing. http://youtu.be/VxzE9k1CzUw?t=30m53s I'm fairly sure that the same goes for Roland. (just a guess though)