Hi and welcome to Knitting Help!
I've only done swatches of herringbone which is a gorgeous stitch. I would study the pattern of sts and see if you can weave the dropped stitch into that pattern. Each stitch is coming through the collar of one of the deliberately dropped stitches. If it's in the last row, it might be easiert to tink back to it. I know that's not so easy to do in herringbone stitch but it's definitely better than starting over. I would also recommend using a lifeline with this pattern.