I play a magic healer mage in Dawn…
Some things that can be done very nicely:
Loud and portentous spell vocals (It’s Dawn, we don’t do moderation, inside voice, or modest)
Invocation of heraldic beasts*
Dramatic gestures, sweeping motions with implements… there’s nothing to stop a spell being as much a dance as a song, and the healing ones take about 30 seconds each anyway (you won’t want to Swift Cast things if not in a combat situation).
While you might well run out of personal mana doing heals, there are several tents on the main field enchanted with “Chamber of Chimes” (or whatever it’s called), which replenishes your personal mana after 15 minutes of quiet roleplaying. I tend to tell stories and sing songs.
As for demand, if there isn’t a bloodthirsty tournament going on in Dawn, or a riotous football game spilling out from the Marches, or a battlefield spilling wounded and tormented back through the Sentinel Gate… there’ll always be skirmishes happening and the Anvil Field Hospital to be staffed…
You can certainly keep quite busy as a main field healer…
*Often done in my swift cast spells:
“Purity of the Unicorn, be cleansed! (Swift Cast Purification)”
“As the Hydra, regrow and rise again! (Swift Cast Restore Limb)”
“Rise Reborn In Pheonix Flame! (Swift Cast Heal)”