Proves nothing.The believers thought Jesus was coming back in their generation. In that case, the bible didn't account for anything to be happening 2000 years down the track.
We've proven Christianity false just by simply existing today.
How do you know they thought his return was imminent? Wishful thinking maybe. Jesus just told them to prepare, witness, make disciples in every nation etc. He said He would return like a thief in the night. Be prepared.
We still believe Jesus will make that return sometime. Maybe not in our lifetimes. Time will tell.