If it was always seasonal, I have to say I standby my statement that it would have been short sighted to invest heavily in an attraction where so many species can only be viewed for half of the year. It is perhaps short sighted anyway. By the admission of two people on this forum the monorail was built whilst monorails were very popular - well they aren't very popular now! They're often viewed as an impractical, eccentric fad.
In terms of what I expect them to do, it's pretty obvious I expect them to correct it! But I am well aware that the funds are unlikely to be there for that to be done, and I won't criticise them of that.
I would argue it's technically one of the least popular attractions at the zoo considering it can only be used half of the year!

It has a distinct disadvantage over most of their other exhibits - which can be viewed at your leisure every day they're opened!
Alas, I digress..
I think there's a difference between an ideal world and the real world. We could argue all we want about whether the monorail was a wise investment in the 1970's, when many, if not most, zoochatters weren't alive yet (myself included), but the short of the story is it exists today, for better or for worse.
In the Northeastern US, most amusement parks and other places with lots of rides are seasonal attractions. It's simply too dangerous to have these places open in the winter due to ice on the tracks, and can produce unnecessary wear and tare on the ride vehicles as well. In that regard, Bronx Zoo isn't unusual for having this attraction only open seasonally, and given the potential for ice on the tracks it likely would not be safe to open in the winters anyways. Given that more and more zoos are either closing in the winter or only opening on certain days anyways, it also seems very reasonable for such a large zoo to have certain of their more costly to operate attractions closed in the winter when crowds are reduced anyways. Most visitors are unlikely to see the entire zoo in one day anyways, and there's plenty else to explore even with the monorail closed. I'm sure you'd rather the monorail closed, than for the Bronx Zoo to decide to close entirely on weekdays during the winter.
Now, in an ideal world, even though the monorail doesn't work in the winter, the animals would still be visible. I am not disagreeing with that fact. However, we don't live in an ideal world, and it'd be practically extremely costly and difficult to create a way to maintain the monorail while having a walking trail in that area. Given how much walking there already is at the Bronx Zoo, I for one think having the monorail for half the year, which is a great place to rest your legs while seeing the animals, is a better (imperfect) solution than if that area was only a walking trail. Of course, if the monorail did close, there's also the very real possibility of Bronx taking the Dallas approach and suddenly having some exhibits simply not longer visible to the public. I'm sure that isn't what anyone wants either.
Perhaps the only possible solution I could think of would be to somehow find a way to make the animals from the monorail visible elsewhere in the zoo during the winter. This is already a reality for the tigers (in Tiger Mountain) and red pandas (in Himalayan Highlands), but logistically I'm not sure if it'd be at all feasible (or advisable) to, say, move a herd of ungulates to another location in the winter so that the public could view them.