I noticed Tony Amendola was listed in the credits. Why? While I guess it's possible the speculation that he ended up at another time mihgt turn out to be true, doesn't haveing him listed at the beginning of each episode kind of ruin whatever surprise they might be trying to build?
Credits are about money. If an actor gets credited in the main titles for an episode, that means he gets paid for that episode and gets residuals from its reruns and home-video sales, whether he appears in the episode or not. (People credited in the end titles get paid for the episode but don't get residuals, or so I understand it.) If Amendola is under contract as a regular cast member, entitled to get paid for the entire season, then he gets billed as a regular cast member.
There have been some shows (like
Heroes, IIRC) where only the cast members actually present in a given episode are credited for that episode; and there have been cases (like the
House finale) where a featured actor's credit is held until the end to preserve the surprise of their appearance. But those are special cases, and what kind of billing an actor gets depends on what their contract specifies. Amendola's prominent enough that his agent was probably able to get a contract that got him paid for every episode, and thus billed in every episode.
Anyway, being billed as a regular doesn't necessarily guarantee your character will return. In the NBC series
Awake that just ended, Michaela McManus was hired as a regular and her name appeared in the opening credits of every episode, even though she only appeared in episodes 1, 3, and 4 and then was dropped altogether. They changed their mind about the role they'd intended for the character, so they wrote her out, but McManus was still presumably under contract for the whole season, so she got credited and paid for the whole season -- which seems like a pretty nice compensation for being written out of the show so soon.