I think Terry will survive long enough for someone to do a well supported, proper interview with him (possibly getting his photographs?)
At the moment he's safe, because either his lawyer (who managed to get his genuine personal details, and who limited the interview) or his appropriate adult is OCG and so they know he's not been capable of assisting the police.
Steve's addiction to OTC and prescription opiates will lead to him being reeled in by OCG who will be able to supply when all doctors and pharmacists are no longer able to. Will he be able to resist?
If Kate is an UCO in plain sight, it's not for AC-12. Who was it she went to for sign off for her covert op in support of Ted in series 5?
We don't know much about Gail Vella yet, but I thought of Lyra McKee especially as it appears to have been a professional hit