Greg,
Taking NAL is not going to prevent you from getting drunk (high), trust me.

There has been the occasional person on here who has reported they don't feel the effects of AL when taking NAL. IMO, these people are in a very very small minority. Most people seem to feel increased effects of AL after taking NAL.
I think most of us here, especially earlier on in our treatment, looked forward to taking NAL prior to drinking as it gave us a kind of green light to just drink what every we felt like drinking. As you move further into the treatment, you start to feel a great deal of security in taking NAL as you know it is helping you to get better. Bottom line: I think the risk is fairly small that you'll just stop taking NAL unless you have bad side effects or something from it.
However, if you honestly feel that you will not take NAL because of depression or the like, then perhaps the implant is the way to go until you get some of your craving under control.
As far as the depression issue goes, I don't think NAL is going to cause more depression. The way NAL suppresses endorphines is a sensation that is difficult to put to words, but it is just barely noticeable. The best way I can put it is it is like eating a favorite dish and noticing that a spice or something is missing, but you really can't put your finger on exactly what is missing. You just know it tastes a little different.
Q