Wiley old second row sprints through the line-out as the opposition catcher (lifted) catches and passes to his scrum half. Must be offside - line-out hasn't finished until the ball as left the line of the line out...
the old "Off the Top" catch'n'pass or te straight tap to the SH causes real problems, because the loose forwards (or ancient locks from time to time) can advance as soon as the ball has left the lineout. In the context of the tap off the top, when exactly does that happen? If it is your standard tactic, don't be surprised if the rearmost player is out of the blocks as soon as the tap takes place.
In that scenario, the ref is in a difficult position because watching a ball 12' off the ground to see when it passes beyond the outer shoulder of the jumpers (all of whom have stepping into the gap) pretty much makes it impossible at the same time to be watching the back man come out of the blocks - especially if you are also watching for interference with either the jumper or his supporters.
Given that, I have to wonder why coaches continue to employ the tactic rather than allow the jumper to come to ground. I guess the answer is to avoid the potential wrap preventing the quick release - but the cost of that tactic is that you risk marginal offsides not being called.
Plus, the same team keen to employ "not engage" tactic to either force a penalty for obstruction OR have a player run round to grab the ball from the player at the back of the non-maul. Again, assume that the non-maul needs to move forward from the line-out before he can run round.
Offside line in the lineout after the ball has been touched is the line of the ball . So yes, the lineout has to end before the non-engagers can go round the back. Of course, there is more than one way in which the lineout can end - but broadly it occurs when the ball or a player carrying it leaves the lineout. Personally, I'd take this to mean either that the ball has moved about 1m from the Line of Touch, or that the feet of all the pre-bound players has moved beyond the line of touch. Others may take a different view.