TransCanada Corp.’s $13 billion buyout of Columbia Pipeline Group Inc. was fairly priced, a Delaware judge ruled Aug. 12, rejecting a challenge by a group of hedge funds to the 2016 deal.

The ruling is the latest in a series that have Delaware court watchers wondering if appraisal lawsuits, which ask the Chancery Court to second-guess a merger price, are still worth filing.

The suit accused Columbia’s directors of selling out investors by arranging a “fire sale” so they could benefit from “change in control” payments. It sought an order requiring the combined company to make up the difference...