If you ignore 3.x classes converted into Pathfinder and only look at core and APG; you have 7 classes that can cast healing spells (Bard, Cleric, Druid, Inquisitor, Paladin, Oracle & Witch), 5 classes can use Use Magic Device to cast such spells from wands and scrolls (Rogue, Sorcerer, Alchemist, Magus & Summoner). That just leaves 7 who have to rely upon potions, magic items and other for healing.
My group regularly plays without a dedicated healer and our DM loves undead. We have all learned how to play carefully and equip ourselves with wands/scrolls/potions to compensate for this. Generally those of us who can cast cure spells will take 1 or 2 for emergencies/after combat, but that's it.
Since your the DM I would suggest taking the NPC out just before a fight (kidnapping, death, etc) and let them combat whatever you fancy that's a little less than their usual CR. See how they deal without their heals. From there you can dial the CR up or down to create the type of gameplay that you both can enjoy. One way to help alleviate the stress of no true healer is to provide potions and wands in place of part of the loot. You can either fudge the loot to add a 2-3 charge cure light wand or straight up convert gold into potion of "x".
Last but not least, talk to your players. Discuss your concerns about their mortality rate should they lose the NPC. After that, if you find yourself with a TPK on your hands, just remember it was their choice (and possibly some very bad/good rolls) that lead up to said event.
Best of Luck
Edit: Healing Belt (MIC 110) for 750gp. 3 charges(c) per day; 1c = 2d8, 2c = 3d8, 3c =4d8 | channel positive energy to heal/dmg touched target.