If I don't finish the missions that expire, do they come back, or is it lost forever?

The bi-weekly missions get archived after the entire cycle is complete. Any progress you make in any of the missions is saved. You have to then complete them fully, in sequence, to unlock the following mission.

How do you get the archived missions? Do they just list with the normal missions?

Yes. Starting with the earliest one you have that is incomplete.

The timed missions should say somewhere that they'll be made available, maybe in all that empty space at the bottom of the mission's box. This gets asked a lot, so it might be a good idea and there's plenty of room in that box.

Understand though, that the missions that relate to holidays do not come back. They may or may not repeat next year as the same or similar mission but are unrelated to the progress you made before.

Just so I got this right... I will be able to start form the first in the sequence once the full cycle is complete (regardless if I started it)?

the trellith missions, yes. the q-pedd missions, no. once theyre gone, they wont be back till next year.

Other biweeklies that are currently in play
Prejor
Zolazin
Mylarai
Kronyn
Genetaar
Xecti

No. If you completed a mission in the chain, then you will start from the next available mission in that chain. So you can't, for example, farm 40 Trelith Comm Relays (20this time and 20 next time)

Got it, thks for reply's

Taltherian and Lazuli were bi-weekly weren't they?

both of those were added as high level missions... the most recent high level missions are the crimson missions. All of the biweeklies have a requirement of about 25 energy per click, give or take 5 energy. they also are always (with the exception of prejor) added to the bottom of the mission list.

I thought so. That's why I don't go all out and say you forgot them