If this conference could get strong attendance and sponsorship and make some money, I'm sure they would decide to go ahead and have another one after all to give the time travelers of the future more than one conference to travel back to. Unless the time travelers of the future want to have a life, in which case they will avoid this conference altogether!
you can tell time travel is possible by the large number of bystanders in funny clothes at historic events, such as bethlehelm two thousand years ago - why do you think there was no room at the inn?