Something else to remember, a marsh fiddler with inspiring song can cast it to heal you're wounded pets then forfeit and repeat until they are at full health again. (same suggestion i was given way back when doing celestial fights)
For those without the Nexus Whelpling I was able to do the battle using the Eldritch Manafiend and Mini Mindslayer along with the Emerald Proto-Whelp. Arcane Blast, Amplify Magic, and Arcane Storm for the Manafiend and Mana Surge, Inner Vision, and Interrupting Gaze for the Mindslayer. When Arcane Storm is up the combo of Inner Vision and Mana Surge pretty much one shots a enemy pet and does more damage to the next pet that comes up.