For all teams (save the Laker Collusionists), the loss of a key player means altered Championship hopes.
Lets make the definition of "key" to mean Big 2 or Big 3 ala Spurs GNobili,....
CornBread Maxwell of the Celts had a GNob type role and was MVP of the 1981 Finals (altho Bird deserved it), then in 1984 Cornbread was key in Gm 7 by shutting down Magic Johnson while putting up great O to boot. Injured in 1985, Red A would go on to put a lot of blame on Cornbread for the 1985 loss to the Lakers due to Cornys **alleged** failure to rehab enough to be 95%+ in the fluke Finals loss. But i don't think you would classify Corny as "Big 3".
1983s LA Flamers had rookie James Worthy go down. But that year he was hardly a "Big 3" member or even "Big 4" what with Majic, Kream, Dick Bavetta, Keith Wilkes 20ppg, Norm Nixon 15/7, Bob Mc 15/5 altho Worthy certainly did contribute at 13/5.
Has NBA history shown this spells the end of a Championship, or even a Finals appearance? Always?
Has there ever been a team to suffer a Big 2-Big 3 member loss and still made the Finals?