Have a look at the Wikipedia article on Binary Black Holes. Essentially when two black holes come in close proximity they are believed to merge into a bigger black hole so you won't get one black hole sitting at the event horizon of another for infinity.
Super massive black hole binaries are believed to form during galaxy mergers
Regarding the answer from the linked question you provided I would be hesitant to pull any one quote/conclusion from what is written there. Although it is a good answer, there are a lot of complexities tied up in it and unless you understand most of it it's quite easy to leap to the wrong conclusion.
For example...
An in-falling observer sees the event horizon retreat before them and they never cross it. However they do hit the singularity in a finite (usually very short!) time as measured by their wristwatch.
This states that "they do hit the singularity" so you could conclude that matter falling in goes past the event horizon and falls to whatever is at the center, but this contradicts the statement that "they never cross it" (the event horizon). How can they reach the center without crossing the event horizon first? Then you may think that maybe from their frame of reference the event horizon changes or is not noticeable? And then you realise that it clarifies with "time as measured by their wristwatch" so time dilation has a part to play. So as the in-falling person approaches the event horizon time for them will slow (as observed by someone stationary and outside the black hole). And extrapolating, at the event horizon time for them will appear to have stopped. If this is the case then it doesn't matter if they hang there for a billion years or fall straight in, either way no time has passed on their watch. By now you're probably thoroughly confused and decided to take the approach that the gravitational forces would rip the person/watch apart anyway so it's a moot point.
Please don't take anything I've said as anything other than an example of how confusing it can all be and that pulling a single statement out may not represent the whole picture.
EDIT:
If something like a "big crunch" occurs, then the lifespan of the universe is finite. What happens to the "stuff" that takes (literally) forever to fall into a black hole if this were to happen?
Note that the "stuff" is observed to take forever (by an outside observer) to fall into the black hole. The observation is done via say light reflecting off the "stuff" falling in and that light is escaping up a large gravity well (so it takes longer and longer to reach us the further down the well it is). At the point of the event horizon the light will take an infinite time to reach us (as light can't escape from within the event horizon). But the stuff does actually fall into the black hole. E.g. if two black holes were on a collision course then at some finite point in the future you would have a single black hole with (roughly) twice the mass.
So for a "big crunch" everything will fall into one single point (or black hole) within a finite time.
