If they match up a safety or a linebacker one on one in man coverage against Gronkowski and he fails to get open, he won't play on offense unless it is a (1) obvious run situation or (2) inside the 20.
When the Patriots are inside the 20, and you match up a S or LB 1v1 in man coverage against Gronk, you will lose. I don't care if Gronk is 50%. His size and catching radius makes it impossible to cover without help over the top.
The Patriots have enough weapons with Woodhead, Hernandez, Branch, Welker, and dare-I-say Ochocinco to drive down the field if the offensive line keeps protecting Brady.