Wild Magic sorcerers get the Spell Bombardment feature at 18th level (PHB, p. 103):
When you roll damage for a spell and roll the highest number possible on any of the dice, choose one of those dice, roll it again and add that roll to the damage. You can use the feature only once per turn.
By multiclassing, feats, magic items or wish, it is possible for a Wild Magic Sorcerer to cast healing spells such as cure wounds.
Can healing damage rolls be considered “negative damage rolls” for the purpose of Spell Bombardment (granting an additional healing die if one of the dice gets rolled at max value)?