I mean, if healing was more extensively required, then healer dps would indeed become 'optional' so they wouldn't really be enforcing them to dps except for high end fights, and people don't tend to slack off in that type of content anyways. Also, the healer dying due to difficulty would be no different than dying on the first week of a patch due to not knowing the fight mechanics - Wipe, adapt, try again. It already happens a lot in leveling dungeons and nobody makes a fuzz about it, because it's expected it can happen.