They both should go. May herself has framed the 2017 GE result as a mandate to deliver Brexit. She manifestly can't and has suffered literally the worst defeat in Parliamentary history. There clearly is no other plan. Quite aside from her Government actually being found in contempt of Parliament and a multitude of other sins, that is enough on its own to go.
And if Corbyn can't beat that shambles of a Government which is only being held together by string and some creationist Ulstermen, and he also doesn't have a plan, he should go as well.
It's honestly like watching a football match where the two managers are Dean Saunders and Dean Saunders.