SK, Warlock and Illy are all part of my current group, I'm very pleased with them. I dropped my mystic for a defiler since there's a lot of synergy between the def nox debuffs/dam and the SK and lock nox damage. But since I'm a 6-man group, I was more interested in her debuffs than heals. I also liked the Defiler AA tree over the Mystic AA tree. But, as I said, I'm a full group, so healing was a secondary consideration for that slot. As far as I can tell, thier healing "oomph" is about the same, with the mystic having more damage attacks vs the defiler having more debuffs.

That said, you'll "need" to bring up a new tank and healer if you change your group. You can betray the Wizard to a Warlock and you want to keep the Illusionist, so you don't have to start those two over. However, mentoring will go very fast and the new ones will be lacking on AAs for a while unless you lock adventure xp. My newbs are around 90AAs at 78. My other toons are all around 120. On one hand, mentoring will let you fly through 1-70, and the 80s will be insanely OP against everything. On the other hand, you will probably blow past a ton of AAs and having to redo the 70-80 stuff is a real drag when only half your team is actually doing the quests. You'll also get a small boost to XP on each toon for having an 80 on the account. So it'll depend on how fast you want to get back to 80, which boils down to "fast" or "very fast".

Also, you can swap shards on your account. I have been doing the daily shard quest in LS on my 80 team and dropping the shards in the shared bank for my replacement toons. I'd highly suggest doing this while you bring up your new team. The daily part takes like 20 minutes {most of it travel time} and can be done in a group.