Tonight's episode was rather inconsequential. If the Doctor and company hadn't gone back in time when they did...it looks like pretty much nothing would have changed. The Doctor was basically just a sightseer for this one - there was no alien menace to fight (they were good guys) and they even had to let the newlywed husband get killed so they didn't screw up history. At least in the Rosa Parks episode, they were actively undoing the efforts of somebody else trying to mess with time - it this episode, not so much.
Johnathan
Johnathan