Always wondered what happens if Ben died as an alien so this alternate timeline by me (Texroth) is the result of that idea. The reason I am using Echo Echo's near death in Absolute Power part 2 is because it is one of the few times I can recall Ben actually coming close to getting killed besides Vilgax smashing Chromastone which we all know the result of.
Warning: This has darkness and death
After Echo Echo was defeated by Ultimate Kevin he is left with a last clone. The clone begs Ultimate Kevin not to kill him but uses a laser blast from his eyes to finish him off. Echo Echo is turned to dust leaving nothing but the Ultimatrix.
Ultimate Kevin stomps on the Ultimatrix damaging it and causing it to go out of control. Kevin's powers get absorbed back into the Ultimatrix and then the watch suddenly disappears. Kevin is now back to normal but Gwen is extremely mad at Kevin for killing Ben. She breaks up with him and then calls the Plumbers to let them know that Ben as well as the Ultimatrix are gone and that Kevin has to be taken away to the Null Void in a cage not made out of metal so he never escapes. Kevin accepts his fate and knows this time he will be in the Null Void for a long long time. Then the whole world finds out.
Ben wakes up and finds out he is Echo Echo on Sonorosia. His symbol is there but he is unable to transform back into a human. He finds the Sonorosian kingdom and immediately realizes he is on Sonorosia. A teenager Sonorosian recognizes Ben and Ben asks him how he can get back to Earth. He reveals that his name is Zevon and Zevon tells Ben to come with him to the King of Sonorosia King Solblast.
They arrive at King Solblast's castle and Ben tells everything but only remembers details clearly until Kevin absorbed the Ultimatrix before saying that he was fighting some big scary monster (which is Ultimate Kevin) and then he found himself on Sonorosia. Solblast tells him that only Azmuth can help him. Solblast gets a spaceship ready so Ben as Echo Echo can return to Earth and wishes him good luck.
The ship is at full speed but Echo Echo and his clones notice the planets they passed by such as Petropia and Terradino. Ben is tempted to turn towards Terradino to scan Humungousaur but decide its not worth it. Eventually Ben spots Jupiter and knows he is getting closer to Earth.
Near Jupiter Ben faces trouble as a space rock hits his ship sending it out of control. The pilot who is the main Echo Echo manages to drive it towards Earth but it will be a crash landing. He then crashes close to Bellwood.
Gwen and Cooper hear the crash and come to investigate and are shocked when they see Ben climb out of the ship. Ben then tells the story of what he believes happened and that he was on Sonorosia before taking a ship to come to Earth. Ben then asks where Kevin is and Gwen tells him it is Kevin who "killed" him and he was sent to the null void because of that and that Cooper replaced him and also that Kevin's powers were absorbed back in the Ultimatrix after it was crushed but Ben does not remember any of this.
Ben has an idea and scans Gwen so he can get his human form back and the scan actually becomes a success and he transforms celebrates being human again with the Ultimatrix back on watch form. Unfortunately this does not last long as Ben times out back into Echo Echo. Gwen however figures out that Echo Echo became Ben's default form and they need to get Azmuth to change it back to human. Eventually Julie also finds out and comes to help. They all go on Ship to Galvan Prime to find Azmuth to help.
Luckily they did not encounter any bad guys since they all believed Ben and the Omnitrix were gone once the world found out and had a pretty smooth travel to Galvan Prime. There they meet Azmuth and tell everything to him.
Azmuth explains that Ben is lucky he died in one of his alien forms and not as a human otherwise he would be gone forever. He then explained that if you died as an alien form you get reincarnated as whatever alien you died on their homeworld but only once. it is a bad idea to die in general because you will lose every form until you scan it again and the Ultimatrix can get damaged after too many reincarnations. Azmuth decides to unlock all his aliens again but warns Ben not to die again because he will not help him the next time. Ben leaves Galvan Prime and is happy he is back but now Ben is half human, half Sonorosian with several Sonorosian traits like sound blasts when he screams, enhanced speed and now sounding a bit more robotic as a human.