Run Focused Winter Tri Training?

Either pick a 1/2 marathon race to do in January and find a plan that is focused towards that, or just follow a 1/2 marathon or marathon training plan over the winter (assuming you are physically able to ramp up your mileage accordingly).  Don't worry about your bike fitness.  Get on the trainer once or twice a week and spin.  Your running fitness will more than make up the lack of time on the bike.  And then get in the pool one or two times a week to help recover from the running and maintain your form.

2 - 3 quality sessions a week in the swim/bike will easily maintain your fitness and form in those two, then you can do 4 or 5 runs a week with a mixutre of paces and workouts.

What I'm saying is that you will not LOSE your cycling fitness and ability by supplementing most of it with running.  Especially in this case where the OP wants to do a run focus.  As I said, a few short quality sessions on the bike over that period will be more than enough to maintain.

The OP did not say that he was looking to boost his bike abilities while having a run focus, only that he wants to maintain.

As for my specific opinion as to overall run fitness translating over to cycling?  I've always subscribed to the "run helps bike, bike doesn't help run" which is counter to what most people say.  I go with that almost purely by personal experience over the years.  All you have to do is look at my bike splits and the amount I train between the two to see that.  By far the majority of my work is on the run and even with less than 400 miles (by race day) in my legs on the bike I still put up a top 2% bike split for the Columbia Tri course.  I put up some huge numbers in my bike splits (comparatively) when you look at the ratio of mileage and time training compared to others.  But I often have a lot more running in my legs than them.

I started my endurance journey with running as a Jr. in high school, and continued with that from '88 - '92 when I got out of the military.  Then I got into purely cycling.

Sometimes I would try to go out and run during my cycling training and it was absolutely brutal!  I had nothing when I ran.  And at the time I was a Cat. 3 roadie.

But now I am running proportionately a lot more and can get one a bike and put up top 5% bike splits without batting an eyelash, even with minimal bike training.  Base can only get me so far, and since there are no other varibles than increased running, I've got no other probable cause (in my opinion) for those splits.

n=2

I spend my winters run focused too, and while my numbers are no where near yours, I have noticed no real loss in overall bike fitness.  It does take me a week or so to ease back into it, but I pretty much pick up where I left off.

I did the winter maintenance - bike focus last winter before starting an IM plan in the early spring and there was plenty of swimming and running.  If my memory is correct, these plans run in the 8 - 11 hours per week with most weeks having at least 2 sessions and sometimes 3 of the other 2 sports. 

The only thing I may suggest is actually starting in the 2nd week of the 8 week plan, assuming you are at that level of fitness, and give yourself some recovery between plans.  More for the mental aspect as the 8 week focused plans are pretty intensive.