MMs are my fave. They shouldn't be dying too often, normally.
I myself take them out on trials and TFs often, including ones that are usually not considered great for pet health (ex, TinPex). Knowing how to control pets, such as use of GoTo to get them out of Blue Pools of Death, for instance, is essential.
Pet durability requires some slotting with pet IOs, management with control, and depends on your power picks:
Bots/FF is essentially immortal, for example. Great mastermind to learn with.
What powers are you playing?
What content are you doing?
How are your pet commands?