I suspect that there are basics we agree on:
Clearly, if we have a tackle then tackle law applies.
If the ball moves away from the tackle zone (>1m from tackle site) then tackle phase is over and we have another phase.
If a ruck forms, tackle phase is over. And if we had a ruck and the ball became clear of it, then the ruck ended and (cos that's how it's defined in Law) we have open play.
If a player plays the ball, complying with tackle Law, then we have another phase.
What is in question is; if the ball remains close to the tackle site, no ruck forms, and no-one plays it are we still in the tackle phase.
I would suggest that the simplest and most practical answer is, yes.
In the scenario described where the ball is still in the tackle zone (assuming for a moment that it IS within 1m of where the tackle took place), but has not been played though is clear enough of feet for the proverbial bird poop to hit square on, that we still regard this as tackle phase.
This keeps the opposition from simply coming round the back, and encourages them to form a proper ruck. This is also encouraged by pinging bridgers so that the ruck can be driven back, and this encourages the tackled players side to commit forwards to it, creating space out wide, OR they seek to get quick ball and we have a fluid and dynamic game.
Allowing opponents to just come round the side seems like a recipe for misunderstanding, and flashpoints, and potentially simply creates a mess.
Further thoughts?