Emslaw whats your take as a practicing lawyer on this. Especially if something went wrong and the BLS hadnt noticed it or patient wasnt still on the monitor.
It gets complicated. Really, lawsuits against EMS providers are fairly rare, as far as I can tell, at least for medical related things (as opposed to wrecking out your rig on the way to the call). That is, in reported opinions. It's always hard to tell what goes on that doesn't result in an opinion or is settled. There are ways to find out, but I will admit I haven't done the research. It would make an interesting presentation someday.
Getting back on point, the question is going to be whether a reasonable paramedic under the circumstances would have done the same thing, one. And two, whether the outcome would have been any different had things been done in the way a reasonable paramedic would have done them.
Say your released patient codes. Presumably, the EMT realizes this and starts CPR, while the medic pulls over and goes to work. The patient dies. The question would then be whether if there had been a medic in the back, anything would have happened differently than it did. It's entirely possible the answer is no. Patients die even in world-class research hospitals every day, and there's nothing that can be done to prevent it. If the answer is yes, though, then there would be trouble.
So, my take is that it would be a very situation-dependent issue. Starting a line on the patient is an ALS treatment, though, as opposed to a mere evaluation, so that might enter into it. If your medical control signs off on you releasing to BLS, then it will be more on him, as the ultimate medical authority.
The best I can do is equivocate. If there's no indication from any diagnostic tools in the field that the patient requires a paramedic, then based on the information available, would a reasonably prudent paramedic still have ridden the call in? If yes, then would the outcome have been any different? A lot of it is going to depend on your local protocols, both the written ones and the way things operate on a day-to-day basis.
For example, NJ is an interesting place when it comes to EMS. Not only because we have a tiered system, but also because we have a dearth of paramedics (something like 1500 active medics in the entire state). In suburbia or the more rural parts of the state, ALS might not always be available. As a BLS provider, I'm expected to have a good understanding of what paramedics can do. The idea that every patient needs a paramedic is foreign to me - and would get me frequent posterior-chewings from the local medics (who expect to be cancelled when my 'chest pain with difficulty breathing' job turns out to be a hyperventilating 16 year old, or something like that). Some EMTs are more 'paramedic dependent' than others, and Paramedics can release to BLS after evaluation. However, the last step in that process is asking the BLS crew if they are comfortable treating the patient. If the answer is 'no', then the paramedic should ride the call in anyway. Is the whole process reasonable? I don't know if it's ever been tested.
Sorry I can't be more helpful.