did Randy die and why did the clowns

1) His brother says "I think he might be alive", so that's a strong indication that he doesn't die after all.

2) Salva's movies are known for being very metaphorical at times. This one in particular deals with fear and personal demons. It is implied that Casey's nightmare (clowns) lives through the escaped lunatics. Not in "it was all a dream" kind of way, but more like, well, a simple metaphor for dealing with your fears. I think this is the reason for the final quote. In a realistic plotline, the lunatics wouldn't attack that house, but they also wouldn't attack the circus and steal the clown's costumes withough being caught or at least noticed.

"We all go a little mad sometimes"
Anthony Perkins as Norman Bates - Psycho (1960)