My X1900XT lasted me from around June 2006 until September 2009. By 2009 I was playing games at medium quality and I was okay with that.
The reason why I replaced my X1900XT with a HD 5850 is because my X1900XT died.
Exactly what happen to me, my 8800GT - died after 2 years and 1.5 weeks (Inno3D wouldnt even help, not interested
I bought a GTX470 on my old X2 4200+ system and was hughely happy, just got a very decent wage one month and splashed out on a completely new rig.
In my opinion, that card will last easy 18months.. (1.5years) - stop worrying and enjoy :-)