I haven't read the comics, but there are actually time paradoxes in the movie series, and obviously the universe in Back to the Future is not destroyed, and so I only can conclude that Doc's hypothesis that the universe will be destroyed by a time paradox is actually incorrect.
For instance, a paradox is created when old Biff from 2015 travels back to 1955 to give his younger self the sports almanac. He alters the timeline so drastically that the events of Back to the Future part one and the beginning of part two cannot possibly have occurred anymore. Doc Brown has been put in an asylum, and apparently Marty lives in Biff tower in that timeline, when in their original timeline, they had taken their trip to 2015 on the same day. Unless some other set of events is in the comics to explain it, it's impossible in this timeline for Marty and Doc to have traveled to 2015 in the time machine in the first place.
I think the only model that makes any sense at all is if in BttF universe, there exist many timelines that may branch from a single point in time, and when people time travel, they may be traveling from one to another, and changes to the timeline are creating new timeline branches.
Further support of this theory, when Doc and Marty discuss how to restore the timeline in part two, Marty suggests returning to 2015, where they can recover the almanac before old Biff ever travels to 2015. Doc rejects this idea, saying that they would be in the 2015 of this alternate timeline. If there were no time paradox, then Marty's idea would have worked. Therefore, since they had come to alternate 1985 from the original 2015 AFTER Biff had made his changes, they must have somehow crossed timelines when they time traveled back to 1985.