Or was it just dumped by NBC on a short notice basis? It seems like Dan Blocker's death and the move to Tuesday nights pretty much sealed its fate.

I have just finished up the last season and some of the plots were a bit slow moving. I didn't know it was moved to another night. Some say the newer shows really pack a audience and Bonanza just couldn't hang on. Season 14 episode 16 was the last episode. So it must have been cancelled mid season.

Even though Bonanza still finished in the Nielsen Top-20 during the 1971-72 season (its 13th), Dan Blocker died of a pulmonary embolism after that season ended, and Bonanza was moved to Tuesdays at 8pm for season 14 the following Autumn. The new All in the Family spin-off Maude was scheduled against Bonanza, and the ratings for Bonanza plummeted in that new slot. The cancellation of Bonanza was announced in early November of 1972; Bonanza and The Bold Ones (which was down to just The New Doctors by that point) made room for The NBC Tuesday Movie. Bonanza ended-up being the longest-running scripted network TV program ever to be cancelled at midseason.

That Tuesday Movie proved to be just a stop-gap measure to fill the Tuesdays at 8 and 9 hours until the end of the 1972-73 season, as NBC the following season would premiere three new dramas in the fall of 1973: The Magician, Chase, and Police Story. (BTW, that Chase is not to be confused with another one-season series of the same name which would also air on NBC in 2011.)

If NBC had let Bonanza finish-out the 72-73 season with, like, 8 to 10 more episodes (provided that its 14th season were still announced as its last in November of '72), there could have easily been a 2-hour grand finale episode for Bonanza (which would have aired around late March/early April of 1973).