[Boromir88]

I'm sort of confused myself about the ending but here's my interpretation of it.

One can imagine the scene in which Gandalf, say, was placed in such a position.

This I take as a hypothetical, "what if?" Just saying, imagine Gandalf having possession of the ring, taking on Sauron, one on one. Then it goes to "balance" the two sides, sort of like at the beginning of a boxing match or football game, where they weigh in on the advantages/disadvantages, strengths/weakness.

On one side the true allegiance of the Ring to Sauron

This would be in favor of Sauron, he has the ring's "true allegiance" he's the "master" of it, not Gandalf.

Then it's the advantages that Gandalf has.

on the other superior strength because Sauron was not actually in possession, and perhaps also because he was weakened by long corruption and expenditure of will in dominating inferiors.

Now we go back to that "what if."

If Gandalf proved the victor, the result would have been for Sauron the same as the destruction of the Ring; for him it would have been destroyed, taken from him for ever.

Just saying, if Gandalf won, Sauron would have met the same fate as he would have if the ring was destroyed (don't ask me why about that, lol, I'm not totally sure why).

But the Ring and all its works would have endured. It would have been the master in the end.

This just says, with Gandalf as the victor, Sauron destroyed, in the end the power of the ring would have endured and as it says "becomes the master." Which I take of as, becoming the "master" over Gandalf. I just basically broke the paragraph into sentences, plus that's only my interpretation, I would love to see how others interpret that last paragraph.