Yes, it can wear off like all other effects, except poison.
However, you can’t really look at Burn and Poison in isolation… (if you DO that Burn is OBVIOUSLY better). The stronger effect of Burn gets taken into account in both the mana cost & any other spell effects that go along with it.
On average (under perfect conditions) burn will deal 11 (10.96) points of damage, given the cumulative chance of 10% to wear off. In practice the troop may hit 1 life point or be killed before the burn deals its full effect, so it’s not going to average 11 points out in the wild, I would guess it will probably average closer to 7-8 points, which is what we’re balancing on.