The progressives haven't left yet because they don't want to walk away from their pensions
Actually, no one will lose any pension either way. Since 1983 the money that is invested in one's pension account is the individual's money. They own it, not the church. Even if one gets kicked out, the pension is still theirs to keep and take with them.
and seniority (for the clergy)
Presumably, if there was a split, there would be large numbers leaving, maybe as much as 1/3. If that happened, the two (new) denominations would still be the 3rd and 5th largest protestant churches in the USA. There will still be need for clergy in both groups. Again, presumably, those for whom seniority was a concern would still have the same sort of seniority in the new group that they had in the old. We aren't talking about a lot of new folk being added from outside.
and from the buildings that they've paid for and built over the years (for the laity and clergy).
Yep, that's a concern, but maybe not as big as many might think. For the most part ever since the Pacific Homes debacle all of the denomination's institutions (schools, camps, healt and welfare institutions) are operated as corporations in their own right. As such, they are already independent of the denomination. i was the chair of the United Methodist Village, a retirement community the church operates in our conference. But the relationship is such that we elected our own directors, hired our own administrators, raised our own operating expenses and capital funding. Our relationship with the conference was as simple as they gave us a few benevolence dollars (and by few I mean roughly $6000 on a $10,000,000 budget), and allowed us to do fundraising using the United Methodist name. Nothing would prevent similar sort of agreements from being made with one or even both succeeding denominations if there were to be a split.
Our polity does not permit a church to leave and take its property, so we all have to wait for a negotiated settlement.
Well, yes and no.
No, the people leaving can't take the property with them. But the people left behind can sell it to anyone they want at any price they want. The trust clause only comes into play when property has been abandoned. Then, and only then, it provides the annual conference's trustees the authority to dispose of it. Until then, if a local church's trustrees wanted to make it a gift to some other Christian organization, like has been done in the past in giving United Methodist church property to another denomination like the Salvation Army, they can.
Another reason why the Progressives haven't just left is that they are winning.
This to is both Yes and No.
Yes, in the United States it appears that their numbers are increasing.
No, in terms of worldwide numbers the conservatives numbers are increasing.
Indeed, one of the things that is bringing this to a boil at the present time is that the Progressives can see the writing on the wall. It is projected that by 2020, there will be more United Methodists in Africa than any other continent. And our African brothers and sisters are much more conservative than anywhere else in United Methodism. Progressive, looking at trends in the US, which is where UM membership is highest, thought that they had the numbers going in to 2012 to make some of the changes they wanted to see made. That they didn't took them somewhat by surprise. They realize that 2016 is make or break for some of these for the forseeable future. It is for this reason that you are seeing some of the debate being not just about theology, but also about church administration. However, if the US can be administratively separated off from the global church, then Progressives will have the upper hand for those who are concerned about the UMC in the USA.
The "absurdity" however is the willingness of your side to destroy the church over gay pastors. Because that's the only serious issue. We already have gay people in our churches and they are quite welcome. If a married gay couple walks in to the church, we don't declare them "unmarried". The ONLY issue is gay clergy. How much damage are you willing to do for this issue?
I'm not sure who the "your side" refers to. I don't know that WiredSpirit feels so differently with regard to gay pastors than you do, Bryan. But, you make some good points here:
[There] are ... people who would kill flies with a shotgun and not care about the destruction as long as [they] get [their] way.
I seems to me that no one side of this issue has a monopoly on the attitude you've identified.