I don't see the Establishment withdrawing support. They have no other options - the PMLN and the PPP have basically painted themselves as 'anti-Fauj' with their rhetoric. If you thought Nawaz was considered anti Army before, I don't think there's any doubt now.
Additionally, people are selling the Establishment short in terms of thinking that they've already thrown in the towel. This is the same establishment that patiently worked through decades of chaos, death and destruction of the US invasion of Afghanistan and the subsequent issues faced by Pakistan without compromising on its perceived national security goals. I don't think you're going to see them back down from supporting Imran Khan after just 2 years knowing the kind of condition the PPP & PMLN had left the country in.
If the ruling coalition does fall apart, this time it won't be because of Establishment machinations, but because of simple politics, where the coalition members will act to save themselves from a perceived 'sinking ship' and protect their interests. If the Establishment does fail at convincing the coalition to stay together, it will do much the same as the other parties - start working on building bridges and repairing relations with the opposition and other political actors to ensure their interests are protected - but it won't be the one to bring the coalition down.
I agree with some of your assessment, but it seems the status quo can't last.
They're also facing a lot of flack from some margins of society for their role in the current status quo. As for the lack of alternatives, while I agree that on the face of it there are none, allow me to present two possible alternatives from their perspective. The first is in house change, same government, new face, IK out, their guy in. IMO favorite for their guy is SMQ, could also be Asad Umer, but I think that this possibility is more remote. The second alternative isn't Nawaz coming back, he's been sidelined, he's too much of a trouble maker. But his brother has shown some real willingness to get back, I can't be sure how good his prospects are, but he's a contender in their books.
So while they have no good options, they do have options. It just remains to be seen how bad things can get, how much pressure they can take. And how much the opposition or the seas themselves manage to rock the boat.
One thing I have thought to hypothesise for sure, and this is only after reading the truth in your post. Perhaps they won't withdraw support without having an alternative already in place and underway. Status quo can't last, but alternative can't be to withdraw completely and let the mess they themselves created cause more problems. What do you think?
He is speculating himself firstly.
Establishment and the Army are not interchangeable terms. I believe even Khan does not get this either.
Also what does PM mean when he says I am The Only Choice, choice for whom?
This is the same Umpire ki Ungli political slogan he used prior to elections as well.
Its not like he is telling this to the people that hey look over 2 years i have rooted out corrupt practices of the government and I am your only choice come elections for a bigger mandate.
Its just kings and their horses and the Army understanding of politics which is what i was pointing out when i said political identity crisis.
Unfortunately for us none of this is concrete evidence of anything. Those who know and understand what he means when he says this. Or what Faisal Vawda means when he brings an army boot and displays it on a news table on TV. Or what Sheikh Rasheed means he says minus 3. Or when Fawad Chaudhry hints at a lack of civilian supremacy. We have no choice but to point to these things.
But for those who aren't convinced, they will quite logically and sanely dismiss our view as conjecture, and find some other convenient or plausible explanation.