I can see how the planning played out.
Fiyero: So you know there are rumors that you'll melt if you get wet?
Elphaba: Really now!
Fiyero: I know! Ridiculous right? That's what I told Galinda I mean Glinda. Anyway, go to my family's castle...btw where have you been staying at this whole time? A cave?
Elphaba: I don't want to talk about it.
Fiyero: Oh ok...anyway, there's a trap door on blah blah blah floor by the corridor leading to the utility closet. I'll some how get that Dorothy girl to come to the castle and you keep her hostage.
Elphaba: Wait...what!
Fiyero: Hear me out! Dorothy has your sister's silver/ruby slippers!
Elphaba: Wait, she didn't die yet and we have no idea that Morrible would make that tornado that some how went through another dimension and picked up a random house in Kansas (how do I know that word) and have it transport into our dimension and aim it directly on my sister's house in a way where her feet are exposed and her slippers are still in what Amazon.com would call "very good" condition...btw did you know she can change the weather? With those powers and her ruthless ambition, you'd think she'd be putting herself up as the Wizard....
Fiyero: Yeah yeah, and you haven't turned me into a Scarecrow yet by chanting some language you never read before and we haven't met since I became a Scarecrow and tagged along with Dorothy....
Elphaba: Well, in the movie I threw that fireball at you...maybe we met some time afterwards in secret.
Fiyero: Yeah, that's what we did. Anyway...Dorothy will be ordered to go to the castle, and not only do you take her hostage and say you want the slippers, but make her scrub the floors.
Elphaba: Make her scrub the floors?
Fiyero: Yeah, with water...and then you antagonize her so much that she'll lose her temper and throw that bucket of water on you. Just make sure you stand on top of the trap door and get one of your flying monkey slaves to activate it.
Elphaba: They're not my slaves...
Fiyero: Yeah...sure...anyway...and then word will spread that you melted and everyone will think you're dead and then we run away together.
Elphaba: Wow, this plan needs a lot of factors to come into play for it to work, but ok. Wait, what about my activism and fighting for Animal rights?
Fiyero: You sang a whole song about no longer doing good deeds and only looking out for yourself remember?
Elphaba: That hasn't happened yet!
Fiyero: Oh yeah. Oh well.
Elphaba: Wait, how can we be together and live a quiet live when you're a talking scarecrow and I'm still totally recognizable as the Wicked Witch of the West and have green skin that NOBODY else in this world has and the word of my evil deeds and looks has been spread throughout the land?
Fiyero: We'll go to some other place outside of Oz where we can just be together where they never heard of you.
Elphaba: Why can't we just do that now? Why do I have to pretend to be melted and stuff?
Fiyero: Because then they'll come looking for you.
Elphaba: But these people are still going to travel and see a green skin lady and word will spread town to town that a green skin lady is hiding out in the woods near their town...and it'll reach Oz.
Fiyero: It's ok, when you "die" Glinda will take over Oz and banish the Wizard forever.
Elphaba: But I will tell Glinda to keep as as Public Enemy No. 1 just so Ozians will have something to unite against and she can use that to her advantage to help the disenfranchised so when people inevitably will see me with my talking scarecrow spouse, I'll still be the Wicked green lady.
Fiyero: Listen just do it, the audience at the Gershwin will eat it up.