It would make international trade more difficult for US corporations, especially if our large trading partners said “you must pay us in euros” or “we will only pay in euros”. But really, it isn’t as if all international trade is dollar denominated. Most trade is not; much trade is done in euros and in renminbi and other currencies, without dollar involvement. The more worrisome question would be, “what occurred to have people getting out of dollars and into euros (or other currency)?”