Much like the Paladin/Warlock comp, you'll want to kill the Warlock while controlling his healer. Banish the Warlocks pet, begin to drop damage into him with your Mage partner, and get ready to instantly CC the druid when he pops out. A useful tip to CC a Druid in Tree Form is to save your Shadowfury to keep him still which prevents him from breaking line of sight to avoid the Banish. This does leave the pet out of a Banish, but use your judgment for which CC you place on the druid. Fear is still an option if you've already Banished the pet for quick burst to start the match.

Copied from the Paladin/Warlock strat but obviously still very relevant to this comp:

Banishing the pet serves multiple purposes; first it will cause the opposing Warlock to take 20% increased damage due to the loss of Soul Link. Second it will prevent the opposing Warlock from using his pet to Devour magic debuffs (Seduce/Sheep) off his Druid. Third, it prevents him from Spell Locking you and your partner's incoming burst.

Mage PoV:

You will want to do the same thing you do vs the Paladin/Lock (DPS Warlock/ Counterspell his shadow school) Toss a Deep freeze on Druid to help with CC.