The "deadline" that everyone is talking about is a false deadline in terms of consequence for fans. The deal could be done in June, September...whenever.
The big push or "deadline" dealt with Free Agency for this off season. Without an extension of the CBA, several triggers as far as length of contract, bonus proration, etc. must be factored in.
The main thing the deadline does is sets the salary cap for '06. A new CBA had a projected cap in the vicinity of $105-110 million. If a deal is not struck, the cap will be around $95 million. Major difference for cap-strapped teams.