Somehow someone will be able to get him back to normal, even risking her life for it, might be Kurumu.
So Tsukune is a powerless human... or ghoul, we don't know for sure. What we know is that Moka infused some of her powers in him by constantly refreshing herself with his blood. It showed on occasions when Tsukune should have died easily but this power protected him.
He even transformed at some point, into something quite strong. Can't remember precisely.
The problem is that with that approach, Tsukune is getting stronger and stronger and loses what his character is and the story loses the contrast he offers in so many situations, being only a weak human in a world of strong monsters. They tried for a long time to show that his other qualities like compassion, love, determination, some wit were very helful to the team/harem, but it was a very long stretch and they were crossing the line everytime he grew stronger.
The last needle, the heart... quite a strong idea isn't it? His true/strong feelings are what make him so different. Transform this, and he's not Tsukune anymore, only another youkai/monster.
You could say that's why the emergency monster in him reacted, to protect the very last of the human thing he had in him. Of course there's also saving his own life.
My guess is that in the future, that monster power he has in him will always be capped, not very different from Moka, except that his monster powers are totally uncontrollable and no one will dare activating them.
Again, for the moment, the story needs a very weak Tsukune, at least it was built that way. The trick is, he will remain weak, but bearing a very dangerous/dark/uncontrollable power.