Yes and no - he is not a tackler, so he has to approach the ball 'through the gate'; but yes, once the ball carrier is brought to ground, both tacklers and tackler assists must release before playing the ball. If the ball carrier is not brought to ground, then no-one has to release!
Interesting, have only had 3 referees that have refereed the tackle assist properly this season ! Biggest non compliance being the tackle assist, having released the ball carrier attempting to play the ball from the wrong side and not entering the "tackle" from the right direction ! This law has been in some 8 years and is still not understood throughout the game by both referees and coaches.
It's not unusual for SOME "older" referees to not be up to date with the latest laws, interpretations and clarifications.
OY! Wind yer long neck in, Admiral!
I've taken some liberties with Womble's post through selective quoting, but the bits in red have the potential to confuse the OP who is trying hard to get his head around all this.
Scenario 1: Blue 12 and Blue 13 both engage Red 13 and drive him backwards. Red 13 falls ov er with Blue 13 on top of him. We now have a tackle, a tackled player and a tackler. Blue 12 as tackle assist must release everything, but having done so
is now perfectly at liberty to play the ball provided that during the tackle he has not strayed in front of his colleague or the tackled player. He does not need to re-enter through the gate.
Scenario 2: As above, but Blue 13 is not engaged. When Red 13 falls over, there is a tackle but no tackler. Blue 12 (still on his feet) as tackle assist must release everything, but having done so
is now perfectly at liberty to play the ball provided that during the tackle he has not strayed in front of his colleague or the tackled player. He does not need to re-enter through the gate.
Scenario 3: As in 2 above, but when Red 13 falls over, Blue 12's momentum takes him a step beyond the tackled player. This scenario is controversial, but I believe the majority would require Blue 12 to exit and re-enter the tackle zone through the gate, and thus would ping him for "illegal entry" if he simply stepped backward over the tackled player to engage the ball from the correct angle.