Conditional past-future

Huevos

Even though going home early is still in the future the situation that removed the possibility was in the past and set in stone the events that were going to happen in the future.

I don't think optilang meant to set it up that way.  I think he's saying that future events are not yet set in stone.

I would have gone home early is a counterfactual.  It says that I didn't go home early.  I think optilang wants to say that the possibility is still open for going home early.  But I may be wrong about this detail.  If I'm wrong in my interpretation, then I see your point.  There is no reason in that case not to use the version with would have.

Huevos

Maybe I would say: If I had known he were going to cancel, I would have been able to go home early.

Me too.  would have been able to go = could have gone, of course.

CJ 

Huevos: «Even though going home early is still in the future the situation that removed the possibility was in the past and set in stone the events that were going to happen in the future.»

This is interesting! So, is Optilangs example correct in this context?
«If I had known it wasn't raining earlier I would have played golf tomorrow.»

«I don't see a reasonable connection between not raining earlier and playing golf a day later.»
Lets assume the rain was so long and heavy that it will take 3-4 days for the loan to dry up!

«Again, my preference is for could, not would.»
Maybe that's because "could have" sounds more like an opportunity already missed, whence a perfect form?

Kooyeen, do you say "have gone play" or "have gone playing"? In this case, I think
the common expression is "have gone golfing".What do you think?
By the way, I was told to use your construction, conditional 3 even though the event was scheduled for sometime in the future.

Kooyeen

I would say something like "If it hadn't rained so much today, I would have gone play golf tomorrow... I planned to do so a week ago, but now the darn grass is gonna be wet for a while, sigh."

The key words here are "something like"! 

You need [would / could] have gone [to play / and played] golf tomorrow. 

The omission of and in the go and VERB pattern is only possible when literally "go" (not goes, went, going, or gone) precedes. (At least that's been my observation.  Maybe you can find counterexamples.)  The verb that follows has to be the same part of the verb as used for go.  Thus,

I can go (and) play golf.  You should go (and) play golf.  I go (and) play golf every week. 

I went and played golf.   You should have gone and played golf.  He is going and playing golf. (This last is not commonly used.)

Those that occur without and are a little more "down register".

CJ