Quantum Theory and the Tardis

I'm currently watching an episode of Doctor Who and per usual they're dealing with a rift in the time/space continuum. This happens from time to time on the show. In this particular episode, Rose has gone back in time to see the moment that her father dies, so she can be with him in his final moments. Of course, at the last second she has a change of heart and saves his life. This is bad. It unleashes these dragons and all sorts of crazy shit. So what happens is the people all team up inside a church and concoct a plan to "set things back to normal". What is strange to me is that this would in effect kill them. Their parallel universe self would cease to exist. And yet they always try to help the Doctor fix things. Don't you think that they would fight back and try to keep things as they are? I'm sure that happens from time to time, but it just got me thinking. If I were a parallel person, I'd want to live, too.