That might have been in the case thirty years ago but certainly not now. First of all, there is no indication that if Castro dies, the political situation between the U.S. and Cuba would change. There is certainly no indication that the gov't of Cuba would change - otherthan it would have a different leader. That, combined with the reality that life in the states is comparitively comfortable - it IS home for the majority of second and third generations - says to me there will be no mass exodus.
However, as I understand it, the hispanic population grows, but the percentatge of it being strictly Cuban, is diminishing. I would imagine David Eduardo or one of his surrogates could expand on this.