We know that a scrum or maul ends when the ball crosses the line. It seems obvious that we should use the same criterion for a tackle. How else would you clarify it? Tackle made in the field of play and both players slide completely into the in-goal area. Do you still apply the tackle law?
That, of course, is exactly the question. But I don't think yuor example of a scrum or maul helps. Assume at a maul that the ball crosses the line for a second, then the maul is pushed back into the field of play. The original maul has ceased to exist, but we now have a new one in that all the criteria are met. It's asking a bit much for a ref to blow Held Up within the 1 second that the ball was in-goal; I suggest that in most cases, we'd carry on with the maul. The scrum is far less likely to happen, as one side or t'other would ground the ball as soon as it hit the line; but if it were pushed back in-field, then we don't have a scrum any more, the scrum having ended and not been re-set. We'd have a ruck. Presumably then we'd carry on with the ruck? None of this is clear-cut.
I like the idea that the tackle ends when the ball crosses the goal line. But what then? As there's no tackle and Bowe is in possession of the ball on the ground, does Law 14 come into play? If so, is it legitimate that the Scottish player can prevent him exercising his options, which seems to violate the spirit of law 14? If law 14 doesn't apply in-goal (I'm not aware of any law to say it doesn't), then does it become applicable when the ball comes back into the field of play (which is almost analagous to the maul or scrum being pushed back). I feel this is such unertain territory that it requires a ruling.