Preem won't have any effect at all on sod. It only affects seedlings.

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Surely they do! Well, not that I'm aware of. Anything that you can spray on one species of plant will almost always kill all varieties of the same species. The TIF mutation is different from common, as you are well aware, but not enough that there are targeted herbicides for one or the other. The tough love approach is to spray it out with RoundUp and replace the dead area with a new piece of Tif 419. If I were going to do that I would measure the size of the piece of new Tif and make a template out of cardboard. I'd spray the area inside the template, let it die, cut it out, and drop the new sod. So if the new piece of sod was 24x36 inches, cut a 24x36 inch hole in a box and use that to protect the surrounding grass from over spray. Remove the box and watch the magic happen. In a couple days you can cut out the old and replace with the new. Be sure to prep the bare soil to make it level before putting the sod down. After you think it's level, walk on it to press down any fluffy spots. Re-level as necessary. Then drop the sod and walk on that again to ensure good sod-to-soil contact. Roots will not grow through the air to reach the soil. When you water the new sod, all you have to do is keep the sod moist. You don't have to saturate the soil underneath.

Where do you live (city/state)? How old is your lawn? What is your watering routine? What is your normal height of cut? How often do you mow? It has been my experience this past summer that common bermuda as hardy as it is, is no match for hybrid cultivars. Withholding water and mowing low was enough to kill back most of the common bermuda in my yard. During the heat of the summer I watered 0.25" every 8-10 days and mowed at 0.25" every two days. The common stuff really died back and let the Yukon take it over. Since your tifway is touted as leap and bounds above my seeded Yukon, I would say that the same could work for you. You just need to watch very closely for drought stress then water before your tif suffers. The common stuff should show stress a day or so before the tif. The low mowing and lack of water turned stolons golden brown. It was too much for it and I never gave it a chance to recover. I just kept pushing it until it was gone.