Cyprus will become a member of European Union on the 1st of May 2004 (in one week) no matter the result of the referendum. The only difference will be weather the Nothern part of the island, currently occupied by Turkey, will join also or not.
I personally think that it is better for Cyprus to get united now than wait for a better plan. It has been separated for 30 years, and it was never closer to reunification than it is now. If it will not happen now, it will not happen for the next 5-10 years. Maybe more.