A little late on this one. But the answer is that a muff (touching of the ball in a failed attempt to possess it) or a tip does not affect the status of the ball.
If a forward pass is tipped, it is still a forward pass and thus dead once it hits the ground. If the offense fumbles the ball and the defense muffs the fumble while trying to recover it, the status of the ball does not change. It is still a loose ball in team possession of the offense (i.e., the offense gets the ball if the fumble is muffed out of bounds). In the same way, a free kick that is muffed (by either team) is still a free kick. And free kicks that go into the receiving team’s end zone are touchbacks by rule.
If a forward pass is tipped, it is still a forward pass and thus dead once it hits the ground. If the offense fumbles the ball and the defense muffs the fumble, it is still a loose ball in team possession of the offense (i.e., the offense gets the ball if the fumble is muffed out of bounds). In the same way, a free kick that is muffed (by either team) is still a free kick. And free kicks that go into the receiving team’s end zone are touchbacks by rule.
In practice, this helps the receiving team, such as when a muff on the 1 yard line goes into the end zone. In theory, that’s not the case. For example, a powerful line drive kickoff could be muffed at the 35 and deflect into the end zone (obviously, I’ve never seen this happen). But if it did, the ball would come out to the 25, not the 35.