Final answer:
The underlying message of Robbie's statement is that he is suggesting postponing the talk.
Step-by-step explanation:
The underlying message of Robbie's statement, "This talk can wait, or just not happen," is that Robbie is suggesting postponing the talk. By saying that the talk can wait or not happen, Robbie is implying that it is not necessary or urgent at the current moment. This suggests that Robbie does not see the talk as a priority and is open to delaying it.