What natural mechanisms could lead to the unlikely case of the same rogue asteroid or planet passing through our solar system twice? I find he following answer to the question What's the soonest Oumuamua could return? unsatisfying and oversimplifying and the last five words "Therefore it will never return." unsupported at a minimum.


  Oumuamua as an object is remarkable, because it has a positive net energy, which means it is not bound to the gravitational well of our sun. Therefore it will never return.


So I'd like to ask: *What natural mechanisms could lead to the unlikely case of a rogue asteroid or planet passing through our solar system twice?"


Stick to accepted scientific facts and theories
Let's give an ample time limit of 10 billion years between visits.
For the purposes of this question, the solar system includes the Kuiper belt (50AU) but not the Oort cloud
Don't include intervention by artificial means or intervention (divine or otherwise)
Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is (Douglas Adams)


The wikipedia page notes that 'Oumuamua "has circulated the Milky Way several times" so it was unlikely to have formed around any nearby star. While it would take 'Oumuamua  600,000 years to travel here from a local star, the time before it can be expected to have another stellar encounter would be much greater, hundreds of millions of years. And the next star that it meets is unlikely to be a currently local star, it could be almost any star in the galaxy. 

Once an interstellar object has left the solar system it will travel in a roughly straight line, (slowly curving with the general gravity of the galaxy). For it to return to the Earth it would have to have a gravitational encounter with another star (or more likely a series of encounters) that send it back towards the solar system. Even given a vast mind-boggling long period of time like 10 billion years the chance of this happening is minute. 

Such an object will probably orbit the galaxy several times between stellar encounters, perhaps it has an encounter every 250 million years. And it is equally likely to encounter any of the disc stars (conservatively 50 billion stars). This means that the mean time between encounters of the sun is on the order of ten quintillion years. 

It isn't impossible.  It is quite easy to design a free-return flight to the moon.   There is no reason why a free-return flight to another star can't be done. However, space is big "therefore ʻOumuamua will never return".