[Someone]

It is worse. "in particular you agree ... to delete tweets that are marked deleted in the future"

Because of that, I do not see how anybody can even think about using this dataset for research.

If you keep all data, you are in breach of the license. If you do not, you are guaranteeing that you cannot reproduce your results in the future.

Als, there is the practical side. I would guess it takes a week to check for deleted tweets, too, so how are you going to comply with that clause?