If you are an ardent fan of the WWE, you more probably than not have encountered people who call WWE matches 'fake'. While these people are not right, they are not technically wrong as well. WWE is a Sports Entertainment show that is supposed to elicit an emotional response from its audience. Let us take a look at how the WWE works.
Imagine WWE to be a dramatic TV show, that is exactly what it is. WWE falls under the category of 'Sports Entertainment', the show uses the sport of wrestling to convey a fictional story to the audience and entertain. The entire show is based on an alternative universe that is supposed to exist only inside the bounds of the show. Every WWE superstar is a fictional character who embodies personality traits that stand out and define their identity.
This is much like any other TV show which has a protagonist, an antagonist, and some supporting characters. Every WWE superstar is part of a storyline. These storylines show us the journeys of the good guys as they try and beat bad guys to get to their eventual goal, which in the case of the WWE is Championship Belts. The technical terms for these characters are 'face' and 'heel'. Let us use a current storyline to understand this - In the Kofi Kingston vs. Brock Lesnar storyline, Kofi is the 'face' aka the good guy who goes out with positive intent and embodies noble values. On the other hand, Brock is a 'heel' as he hurts people with little reason and embodies character traits which are generally perceived to be negative. Therefore, 'Kayfabe' refers to the entire alternate universe of characters that only exist inside WWE and includes everything from the rivalries to the relationships that may be shared between superstars.
The wrestling in WWE is both - real and fake. The maneuvers that the superstars use are very real but they are practiced in a way that they do not critically hurt the performer receiving them. Wrestlers rehearse their matches before shows and are supposed to know what their next move is. WWE fights are more of a theatrical performance where the fight is used to entertain the audience with outrageous stunts and moves while the fight's result drives forward the storyline which will lead to further fights. Weapons like chairs and ladders are specially made so that they hurt less and are also used at angles and speeds which reduce impact. Sometimes, these moves go wrong and the wrestlers actually get hurt. There are special signals that the referees use to signal the medics and let them know if a performer is 'actually' hurt. Props like fake blood are used to magnify the perceived impact of the fight. Sometimes performers may bleed real blood through 'blading' but the process of 'blading' is severely condemned in the WWE and other wrestling promotions.
So, to answer the simple question...
Can the Undertaker actually come back to life after being buried alive? Yes, but only on your TV screens.