If you have friends and a good guild to group with in Secrets of Faydwer, you won't feel a difference in SoD with Mercs. I think the class/role that gets hurt the most with SoD, is the Healer Box. But If your question is regarding pick up groups, I would say they already dried up in the lv 70 era.
As a main cleric it had little to no negative impact on me. What I did see was a lot of box clerics get shelved but also players were able to go off and do things without having to box a cleric or wait around for a cleric. Now I am able to join a lot of "in progress" groups so they dont have to have a merc healer.
It does nothing to impact cleric mains. All it does is relieve the need to have a box'd healer in times where you only have a couple people or solo.