Illumina Inc.’s acquisition of cancer diagnostic specialist Grail Inc. is on go in a $7.1 billion transaction that is structured so that it can be unwound with limited impact on Illumina. However, a number of regulatory entities are closely scrutinizing the deal for a potential regulatory challenge, a fact of life that shaved nearly 10% off the value of the company’s shares in early Aug. 19 trading, and which could ultimately scuttle the transaction altogether.