The Knicks are an expansion team in the NBDL this season, which at first glance would seem that it makes it easier for Mayo to catch on with them. However, Westchester participated in the expansion draft back in September, and as a result, they added the rights to 16 players to their roster already.
The Knicks announced a roster of 16 players for training camp shortly after the draft, but they will have to cut that roster down to 10 by Thursday, November 13th. On that roster are Thanasis Antetokounmpo, who was selected by New York in the 2014 NBA Draft, as well as Langston Galloway, Orlando Sanchez, and Jordan Vanderberg, who were all recently a part of the New York Knicks' roster for training camp. I think it's a safe bet that all four of them will make the Westchester roster, leaving six spots open. Mayo will be competing against five other guards for a roster spot, including Joseph Bertrand, the first NBDL Draft pick in Westchester history.
Mayo appeared to be ready to return to Marquette for his senior year when the 2014 spring semester ended. However, he announced his departure to pursue a professional career in late July. It remains possible that Mayo's departure was not completely voluntary.
In other Marquette/NBDL news, it appears that Vander Blue is out in Los Angeles to join the D-Fenders roster. Blue had a cup of coffee in the NBA last season and seemed to be fairly successful in his time in the NBDL as well, so I think he's a safe bet to catch on there.