Using the moves here will 'revive' the Giga Draining pokemon, kill the Destiny Knotting one, and then force a switch for both users. To replicate:
1) Use Speed Boost Sharpedo with Destiny Knot, Protect & Volcarona with Giga Drain
2) Turn 1: Sharpedo Protects (activating the Speed Boost) & Volcarona Giga Drains (fails)
3) Turn 2: Sharpedo Destiny Knots (first to move due to Speed Boost) & Volcarona Giga Drains (killing Sharpedo and itself).
Results: Both Pokémon will faint, then once the user with Sharpedo is moved to the 'Select a Pokémon' party screen, Volcarona is alive with the HP recovered from Giga Drain. Its user is also forced to switch, as Volcarona is marked fainted in his party.