Why was it necessary to rescue Saito from limbo?
In Inception, one of the last scenes (and actually the very beginning scene) is Saito being approached by Cobb to both retrieve him and remind him about their arrangement.
But did that action really matter, besides getting Saito out of limbo sooner than him just dying in Limbo (is that even possible, hence the problem with being so deep?)?
It seems that without Cobb directly rescuing Saito from limbo, he would have just died of old age, woken up in reality after mere minutes due to time dilation theory and shaken it off. It would still have worked out fine for Cobb. Saito experiences a few extra years of subconscious deep level dreaming, but in reality only a few minutes later... still wakes up and can "make the call" before the plane touches down.
Why was it necessary for Cobb to go looking for him and drag him out of limbo forcefully?
Best Answer
Similar to what The Wandering Dev Manager said, the entire problem with this situation is that the sedatives to support a multi-level dream are too strong to be woken up simply by dying. You need the kick. If you do die in a dream supported by these heavy sedatives, you enter Limbo.
The same principal is at play once you're already in limbo. If you die in Limbo without receiving the kick, you don't wake up. You go a layer deeper into the dream.
Even though Limbo is "the deepest layer," it's already revealed in the movie that Limbo isn't just one layer. When Cobb and Ariadne go a layer deeper to get Ficsher, that is deep enough to be considered Limbo. However, when Cobb dies in that layer, he goes a layer deeper into another layer of Limbo. Therefore, Limbo is a multi-layer reality with (potentially) an infinite number of levels going deeper and deeper and becoming harder and harder to wake up from.
This shows that the reason that Cobb needed to go back and retrieve Saito (and the reason that once Saito died in the dream, it was a very time sensitive matter) is that if Saito had died in Limbo, he would have gone another layer deeper and been even harder to eventually retrieve.
Pictures about "Why was it necessary to rescue Saito from limbo?"
Why is Saito in Limbo?
When Fischer is shot by Mal, he is unable to help him and Fischer dies, descending into Limbo. Afterwards, Mal is killed by Cobb, and Eames asks Saito to hold a grenade and protect Fischer while he sets up explosives. After using the grenade to kill many projections, Saito dies, and goes into Limbo.Does Saito get stuck in Limbo?
Cobb and Saito are both stuck in limbo, and according to someone on the team (can't remember who said it) limbo is a place you don't want your mind to be in... but some how Cobb and Mal once managed to get out of it without returning back to the real world as "vegetables" by killing themselves in the limbo world.How long was Saito stuck Limbo?
Therefore, Cobb and Saito would have been trapped in limbo for 182 years if they hadn't been kicked out of the dream.What Saito wanted in Inception?
With Nash gone, Saito makes Cobb an offer. Rather than extracting information from a rival's mind, he wants Cobb to leave something behind: an idea, so neatly camouflaged that the target will never realize where it came from. In a word, inception. Specifically, he needs Robert Fischer, Jr.The Escape from Limbo, Inception ending, Deja Vu
More answers regarding why was it necessary to rescue Saito from limbo?
Answer 2
You need the kick
Wikipedia:
Cobb reveals that while dying in the dream would normally wake Saito up, the powerful sedatives needed to stabilize the multi-level dream will instead send a dying dreamer into "limbo", a world of infinite subconscious from which escape is extremely difficult, if not impossible, and a dreamer risks forgetting they are in a dream.
So it seems that the only way to escape from Limbo is via a kick (in this case from Cobb's gun)
This is similar to Mal and Cobb, who died of old age in the dream world but had to get the kick from a train to return from Limbo
Answer 3
I'm not sure anyone in universe knows what happens if you die of old age in limbo.
Cobb certainly thinks it's important Mal and him die to escape, but I don't think he knows what would happen.
My interpretation is that the place slowly drives you crazy and you would still be that way when you return to the normal world.
In addition I'm not sure he would have felt like making a call after being abandoned for decades.
Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.
Images: Harry Cooke, Charlotte May, Mikhail Nilov, Erik Mclean