Health Swap Mechanic in HearthStone

Reversing Switch will use the buffed stats of 3/2, boosting Cogmaster to 4/3. In effect, the Cogmaster's buff will be applied twice. The mechanics of this can be found in the description of Crazed Alchemist.

The Battlecry works by taking the minion's Attack and Health values, and creating an enchantment specifically granting the minion the opposite values. Because this enchantment is created based upon the minion's current values, any bonuses such as other enchantments and auras (such as the one granted by Stormwind Champion) are incorporated into the enchantment. The enchantment will sit 'on top of' previous enchantments, overriding their effects on the minion's Health.

However, because auras are automatically re-applied following each game event, once the new enchantment is granted, any aura effects will be reapplied, on top of the Alchemist's enchantment. This allows minions with Crazed Alchemist's buff to effectively benefit from auras twice - once through their inclusion in the Alchemist's buff, and then again through being reapplied after the buff has been granted.

When all mechs are destroyed, the Cogmaster would revert to 2/3 (assuming no injuries)

Because the Alchemist's buff overrides any previously applied stat-modifying buffs and sets the minion's stats to specific values, the expiry of any previously applied buffs will not affect the minion's stats. For example, a minion affected by Abusive Sergeant's Battlecry which is then buffed by a Crazed Alchemist will lose the Sergeant's buff at the end of the turn, but will not lose any Attack or Health as a result.