The point is not whether it says "unless they leave", the point is that it does NOT bind the states into the Union, as you originally suggested.
You'll have to dream up another fiction to bind the States to the Union involuntarily.
The guarantee is restricted to only States "in this Union". It is not an "unrestricted" guarantee at all, as you said. Those three words are a qualification of the Guarantee. You can't hallucinate your way out of that. Those three words acknowledge that a State can be in or out of the Union.
You can't make it say any thing about binding the States to the Union. There is nothing binding in that text. It pledges a service to the States that choose to take advantage of it.
The Articles of Confederation were a failure.
The states -voluntarily- transferred some of their soevereign rights to the federal government--because it was the onlt thing that would work.
They knew this, and they made no bones about it.
Of course, your opinion bucks that of the president of the Constitutional Convention, George Washington:
"In all our deliberations on this subject we kept steadily in our view, that which appears to us the greatest interest of every true American, the consolidation of our Union, in which is involved our prosperity, felicity, safety, perhaps our national existance. This important consideration, seriously and deeply impressed on our minds [at the constitutional convention] led each State in the convention to be less rigid on points of inferior magnitude...the constitution, which we now present, is the result of of a spirit of amity, and of that mutual deference and concession which the peculularity of our political situation rendered indispensible."
George Washington to the Continental Congress September 17, 1787
The states were not --involuntarily-- yoked into the Union. Your statement is false.
Note also that this date, 9/17/87 is generally considered the birthday of the Constitution.
You know, I'd much rather have George Washington on my side than you.
Walt
The point is not whether it says "unless they leave", the point is that it does NOT bind the states into the Union, as you originally suggested.
If it doesn't bind the states, it gives the federal government perpetual say over the form of their government. That is, if a state should try and adopt any government other than a republican one, the federal government is empowered, under this clause, to intervene, and by implication, change any non-republican state government to a republican one.
This is just another example of how the states are not, and never were, completely sovereign under the Constitution--from day one.
Walt