If many timelines exist .That could be remedied easily.plz be aware that one logical reason for governments to not allow time machines is the possibility, that many people go back in time and make changes against each other..lets say I go back help Italy win football in 2009 and u go back try 2 help Germany win...and many others go help others win....that would make our present a big mess....
Therefore, my humble perception is that one can only go back and see what happened, but cannot change anything...