I have purchased businesses and we either live with the contracts in place at time of signing or we buy them out and pay the early terminitation penalty. That is what DD is for to determine what obligations your are purchasing and which ones may have clauses to let you out or them out of the contract. That is how it works in the States anyway. This statement is based on my personal experence only.
You are merely making assumptions without any foundation. You are guessing that the agreement contains some escape clause in the event of a merger. Typically, that would not be the case. Typically, it would be silent and therefore the surviving company would assume all of the obligations of existing contracts.