Looking for a book from the 1950s or early 1960s similar to Andre Norton’s Star Rangers, but I don’t think it was Star Rangers. Spaceship with mixed aliens is escaping from interstellar civilisation’s collapse and after various struggles lands on a planet covered in a single massive city. The planet is deserted apart from them and they eventually decide to stay. This is the end of the story as they hope to avoid the chaos by remaining quietly in the city on this planet. So, similar to Star Rangers but my (admittedly old) brain says it wasn’t that book 
Ring any bells?
Ring any bells?
