It would work if, and only if, boss fights were drastically simpler (if not easier).
As most MMOs are now, the bosses are designed to cause groups to wipe repeatedly until most of the group understands the mechanics. Such a design philosophy would essentially make it impossible for anyone to actually get through end-game content.
I wouldn't be opposed to playing a hardcore-mode MMO, it would just require some basic design changes, and boss fights would have to be resettable without a wipe.