Being Omnipotent means you can do anything and everything. You have a few things mixed up though.
I will give you and example of a verses thread I saw one time. It was Goku vs The One Above All. He is a true omnipotent and can literally do anything. Well one person said well since an Omnipotent can do anything, that means they can lose to Goku, therefore Goku wins. This is kinda what you said. Well he could also win. The thing with omnipotents is that they can allow for anything to happen. If they wanted to let Goku win, they could have. They can also chose to win. Why would an omnipotent chose to die?
You also mentioned creating a Goku who is stronger. One, Goku has a finite amount of energy and could never match someone who is an omnipotent. Two, an omnipotent cannot make something stronger then itself. That is because an omnipotent is infinite. There is nothing bigger then infinite. Therefore it cannot exist.
In short, the impossible is possible if they allow it to be. Since an omnipotent will never allow for that, it is not.