Hopefully they're okay. They might've just lost power due to storm damage in the area.
In some cases, the DCs are absolutely astonishing. Had a healer drop to the last boss of The Twinning last night, clearly new, they got told what to do, but the other DPS decided to wipe the fight anyway even though we were right on the verge on clearing it. We go back in, this time the healer drops again about halfway through the fight, then about less than a minute later, DC's and never comes back. So we play the rest of the fight out anyway and finish the dungeon because Clemency has no right being as good of a heal as it is.
I should note that the healer wasn't lagging or even once had a DC icon over their status. They just straight up closed the game.