@Kits3 previously I talk that you was joking, but now I see that you talk seriously.
Sorry but while it's true that no one in this moment can know something concrete about this character (so no one can say "there is no doubt about it"), from another side it's also true that your hypothesis should be treated like the one with less chances to be true. This not because Lauren can't return in the story (in fictional stories there is always a way to make everything possible), but very simple because your scenario include too much elements imagined and without an effective reply with what happened previously.
How much times we have seen Donovan interested to Leon (or Leon only being part of the DOATEC plot)? And how much times we have seen the organization interested to the cloning and the powering of Kasumi or anyway uniquely ninja people? This should give a precise answer about what is more likely to expect from this character.
I'm not saying that Leon will not end to be a character treated with more importance in the future of the series (on the opposite I'm convinced of it, TN seems really fond of him more than Ein or Tengu), but untile now there is really no hint for the happening of your - few realistic but really nice in my opinion - scenario.