Maybe there was a possibility that he could have made a second trip to 1912 after being yanked back to the present. If only he hadn't made one all-important mistake while he laid there in bed, desperately trying to return to 1912. He was still clutching the penny, a piece of the present that Finney said should be hidden away and the very thing that threw him back to 1980.
shareI always interpreted his inability to get back to 1912 as being because he knew he would fail. When he was initially able to go back in time, it was only after he had seen his signature in the hotel register from 1912. That told him that he would eventually succeed and it gave him the confidence he needed to get in the right mindset. However the fact that Elise had given him the watch as an old woman told him that he would, and did, fail the second time. That doubt created a kind of a self fulfilling prophesy.
shareThis is my interpretation as well.
shareI don't dispute that everything unfolded as it should have. There weren't any paradoxes other than the ontological paradox of the watch that was never made, never destroyed, never wore out. But it would still have been possible for him to return to 1912 once more and go back to the future, leaving the watch behind again. It wouldn't have made for as good a story, but it would have been a remote possibility if only he wasn't still clutching the penny. He should have realized that and ditched the coin. Then again, he probably was so distraught that he wasn't thinking straight.
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