Is the thief absolved if he repents and returns what he stole, while not being certain that his friends have returned the amounts they stole?

If you all collaborated in the theft and divided the stolen goods, then the repentant one must return the entire value of the stolen goods, and then he can reclaim from his partners what he paid on their behalf, because partners in theft bear responsibility for one another. However, if each person stole individually, then each thief is only responsible for the value of what he stole, and the questioner's responsibility is discharged by what he has done in returning his share and advising his companions.