D&C 76

Of those that will reside in the telestial kingdom, the Lord said -

 "These are they who received not the gospel of Christ, neither the testimony of Jesus."  (Doctrine and Covenants 76:82)

"These are they who are thrust down to hell."  (Doctrine and Covenants 76:84)  (which I believe are those that are in hell in the spirit prison)

"These are they who shall not be redeemed from the devil until the last resurrection, until the Lord, even Christ the Lamb, shall have finished his work."  (Doctrine and Covenants 76:85)

But even so -

"...thus we saw, in the heavenly vision, the glory of the telestial, which surpasses all understanding..."
(Doctrine and Covenants 76:89)

I believe that through all eternity, we will still possess our agency.  The Lord said -

"For behold, I, God, have suffered these things for all, that they might not suffer if they would repent;
17 But if they would not repent they must suffer even as I..."  (Doctrine and Covenants 19:16–17)

In my mind, having their agency and thus the capacity to sin, if they will not learn to repent (maybe due to pride) they will continue to suffer for their sins through eternity