ok just to explain; yes i accept charlie is dead, as in you and i are not, nor are jack kate sawyer etc..i was disinclined to admit it, but im just fucking around there.
from the flash forwards, one may also conclude that the passengers did not "die" when they crashed; they are physical beings, alive, and in most all regards, live and well; it would seem they are "real" people that are stranded in some island-place which possesses or is inhabited by some as of yet undetermined unusual power/s. so in that reality, charlie drowned. dead. gurgle, gurgle, twitch- dead. il est mort.
Also, jack's father i now accept to be dead in the same regard.but we see christian manifested as though he were living in season 1 when jack thinks he saw his father in the jungle, and in this most recent episode, we see him again giving a message our favorite canine lab on the cast. he is able to appear and communicate, which would seem to be the same situation charlie has gotten himself into.
as for dave, i've not seen the episodes with him very much/wasnt paying as much attention, but he would seem to be not as real as christian or charlie at this point; no one else acknowledges his presence save for reyes; it would lead me to conclude that dave is either some devilry of the island's machinations, or an (most likely) otherwise significant anomaly attributed to the unfortunate hugo's feverish and otherwise afflicted mind.