In existentialism, it is thought that man is cut off from external authority and therefore, all morality needs to found and determined from within each person. Each person is, first and foremost, responsible to himself. The other key to existentialism is that man must take active action in his life in order to be existentially alive. If man is passive and lets the whims of others determine his fate, he is existentially dead.
With that in mind, you need to consider the morality of the characters in the play. You need to judge them for yourself, but here are a few things to review as you evaluate the play.
1. How responsible are Ros and Guil for what could happen to Hamlet in England AFTER they accidently read the letter?
2. How responsible is Hamlet for their deaths when he changes the note?
3. How does Ros and Guil betting the player with games they KNOW they will win contribute to this theme of right and wrong.
4. How do Ros and Guil feel about their sitation in the end -- especially when you consider things they say such as, "there must have been a time when we could have said no."
5. How equipped are Ros and Guil to really have a basis for judging their actions or the actions of others as right or wrong? Are they not just characters in a play?
6. What do you make of the player -- he seems to know what is going to happen to Ros and Guil but he doesn't/can't do anything about it.
This list should get you started -- the play is so rich with irony and existential thought -- Enjoy!