Tyreese should be in it for the long haul. He's introduced way earlier in the comic and was Rick's right hand man and go to guy. In the comic Tyreese was with Rick and company when they found the prison. He didn't accidently happen upon it like on the show.
Even though he was introduced later in the TV show, I think his character will grow and he will become a very strong addition to the group.
3/20 - Dream Theater