The Sun System Handbook on of sunsolve.sun.com has an End of Support Life list on it, you must have a Sun support contract to get to it.
The E450 server end of support life listed is 31 December 2010. Normally Sun ends official support of a product ~5 years after the last ship date of the product. In the case of the E450 last ship was in November 2002, so the service seems to be available a bit longer. Of course finding parts for older systems in a quick manner may be an issue.
HTH