Blanchett had been at Edgar Street since the start of September while Dennehy arrived back in the summer but they have now returned to Peterborough and Cardiff respectively.
Their departures leaves boss John Trewick short of two more defensive options and, with Blanchett a regular at the heart of his backline, means changes must once again be made at Plainmoor.
But the Bulls boss has received positive news among his injured defenders. Ryan Green is hoping to be involved having missed the last two games with a leg problem before suffering a cut to his head last Friday when he was attacked with a bottle in a pub.
The postponement of last Saturday’s home clash against Lincoln has given also given defenders Richard Rose and Ryan Valentine a better chance of being involved after they missed the Johnstone’s Paint Trophy defeat to MK Dons last Tuesday.