On an AOL DS message board, I tackled the tricky thing about the massive change in history caused by Barnabas, Julia and Eliot in 1840/41 by coming up with a scenario (had the series continued). It was a whole plot-line, along the lines of Charles Delaware Troll's wonderful website. I'll keep it short so as not to bore anyone and not to violate our fantastic message board's rule about not delving into fantasy role-playing and storyline matters (there are other boards for that, as our illustrious webmasters point out).
When our three heroes return to 1971, they find that the family they knew is gone; they never existed, since the lineage had so drastically been altered. Instead, there is a completely different Collins family (all played, of course, by the actors/actresses on the show). Our heroes manage, as usual, to ingratiate themselves into the new family, wondering what to do now, finding themselves strangers in a strange land. A severe haunting begins, which leads to the eventual deaths of virtually everyone in the family. It turns out that the main spectre is none other than Tad Collins. It's perplexing why he would do so (there are also some "minor" ghosts involved), since history records him as being a great man, involved in the abolitionist movement, dying in a tragic accident in 1860. But he has a dark secret, one for which he will go to any length to keep hidden, even as a ghost. There is a subplot intertwined with all this - since Barnabas sent back only his consciousness and not his body to 1840/41, when the three return to 1971, Barnabas in his 1840 body, they find his 1970 body a very much alive but mindless/soulless zombie (two Barnabas' for the price of one!). To cut to the chase, the three go back in time to 1860 to find out what really went on and why the evil, enraged spirit of Tad Collins did such mischief in 1971. They solve the mystery and get things straightened out, including restoring the "correct" family lineage, so when they return to 1971, there's Elizabeth coming into the drawing room, looking for Roger's speech which he needs to give at the history society meeting. And away we go with all new adventures as DS continued on the air for years and years and years. It was a lotta fun coming up with the whole story.
Gerard