Master's Summons

I'm quite late, but what the original commenter was calling "overpowered" was if this could bring back a sentinel from the dead, not sentinels themselves.

Sentinels are not overpowered in any sense of the word and probably never will be as they are mostly used for build synergies like synth fiber/deconstruct + equilibrium and/or utility. (Even Dethcube, which markets itself as an "offensive sentinel", is mostly used because Vaporize can seemingly stun just about anything in existence and energy generator can be helpful.)

But if Master's Summons could bring back a sentinel from the dead you could potentially infinitely farm rare resources with the mod "Spare Parts" by going into a high level mission with a super squishy sentinel and letting it die then reviving it over and over again. Allowing for potentially MASSIVE amounts of morphics, neurodes, gallium, orokin cells, neural sensors, control modules, tellurium, or even argon crystals and entrati lanthorns all to be farmed infinitely and quickly. It could also allow using a sentinel that has fully invested in bulk as an infinite revive with "Sacrifice" like people can already sort of use Djinn and Protea Dispensery Augment for.

This is why Regen simply stops your sentinel's death and heals it instead of letting it die and then reviving it. This is why Hard Reset has such a strict activation condition and why it's still one of only 3 things which can revive a dead sentinel, the others being Djinn's Reawaken and Protea's Dispensary Aument both of which are both on long cooldowns. 1 mod makes reviving your sentinel potentially a crazy good farming method for things that are supposed to be rare, and another would allow endless revivals on any frame at VERY low cost, every other self revive requires enemies to kill like Unairu's Last Gasp and Sevagoth's passive, a resource like Nidus's stacks, or a cooldown like Voruna's 4th passive. This would require 50 energy, and a sentinel that can survive long enough to complete the revive process. It work on ANY frame as well, so any of the ones that can easily make back that 50 energy could do it forever.

Personally, I would be absolutely chill with Spare Parts (and maybe Sacrifice too if DE is understandably wary of it as well) being completely reworked or even removed if it meant reviving a dead sentinel isn't something that DE has to be scared of breaking the game with. I built mine with 8 utility mods, so it always sucks when it dies and that utility VANISHES. I'd be more than willing to give up an ability slot just to get that utility back.