The Tribune/Dish dispute, unsurprisingly is now the longest TV dispute, EVER, surpassing the CBS & CW O&O/TWC/BHN dispute that took out WTOG-TV in Tampa among other stations, like WCBS-TV in NYC! Wow, Dish, and you almost "secretly" threatened to blackout the Calkins trio after they merged with Raycom (who was in a dispute).
By the way, could've the Calkins trio (WWSB/WTXL/WAAY) been blacked out from Dish after they were sold to Raycom?
The longest major one. There have been smaller ones (involving owners that own one or very few stations). The Buckeye/Sinclair dispute took WNWO off Toledo cable for something like six months, including the 2014 Winter Olympics (Toledo still got to see most of the marquee events via CBET, which was already carried prior to the WNWO dispute)