OMAHA, Neb.—Warren Buffett’s company is abandoning its purchase of a natural gas pipeline from Dominion Energy because of uncertainty about whether the deal could get regulatory approval. Berkshire Hathaway Inc. will receive a $1.3 billion refund on the proposed purchase of Questar Pipelines that was also supposed to include $430 million of Dominion’s debt when it was announced a year ago. The Richmond, Virginia-based energy company said it still plans to sell Questar and will work to find another buyer by the end of the year. Dominion also said the decision won’t affect its financial outlook. Separate from the Questar pipeline deal, Berkshire did buy $2.7 billion worth of Dominion’s natural gas transmission and storage assets last year, which included more than 5,500 miles of natural gas transmission pipelines and about 775 billion cubic feed of gas storage facilities. Berkshire also took on $5.3 billion of Dominion debt as part …