Clerics aren't required because you can't typically fight the HP drain of combat with healing spells, even with one, unless your DM's softballing the party. Healing spells definitely can't deal with the party getting hit by high-level AOE's. A 1d4+5 Mass Healing Word won't compete with an 8D6 (28 avg) fireball for hitpoints, even though they are both level 3 spells. Not even a level 3 3d8+5 Cure Wounds spell can (only 18.5 avg). 

5e epitomizes the principle of "A good offense, Period." I have trouble looking at a Divine Soul Sorcerer seriously because of this, since they give up some pretty powerful options for a short list of some of the weakest (heals), most financially expensive (revives), and/or circumstantial effects (restorations).