Checked in game, the pet health is very low, at most 9. As evidenced above from an in era source and collaborated shortly after its max health should be in the realm of 100-150.
"USES, By Onigami (1/28/2001)
This spell is a fancy DoT spell.
It melees like a pet for 700mana, but doesn't tank. The only HP it has, is probably to absorb damage shields."
As we can see here, the pet shouldn't be getting insta killed by low level damage shields.
I feel this is corroborated by a later post, which acknowledges the pet is mainly a toy, but also insinuates the pet can stand up to the wizard DS which is cast on most frogs in Seb:
"NOT AT ALL USEFUL...MERELY A TOY, By Meself of tarew marr (1/28/2001)
This spell is only useful as a toy. It does approximatly 700 damage vs. a 52+ mob in Sebilis, making it extremely mana-inefficient.
Interestingly, though, the cleric's hammer is smart enough to move on to the next mob when one falls, whereas this one just dies when the mob it's working on dies over."
As it stands the pet doesn't really have a shot to do anything more than one underpowered hit to anything with even a basic DS, let alone 700+ damage to something returning 2dmg/hit.
Edit: further evidence xuzl pet should have 100+ hp
"Taroo
Station Member posted 01-24-2001 08:00 AM
+ Flaming Sword of Xuzl:
At level 8, a magician gets a pet for 80 mana which will stay more than 1 fight, has over 200 hit points and will root the target. At level 59, wizards have a 700 mana 200 hitpoint pet which DEFINITELY won't last more than 1 fight. Perhaps you could lower the casting cost to 40-60 for the spell?"