Is surrender undoable? If not, then it shouldn't be.

[Hubert L. Bunkerton]

Alright, so a quick anecdote:

I was playing a 3v3 deathmatch game. Our crew did okay early on, but soon the enemy took the lead. For some reason, on both teams exactly one ship surrendered, turning from a 3v3 to a 2v2.
My crew was carrying the team in a junker, while our ally, a goldfish, was having some trouble.
The score got ridiculously close, as we made a comeback and only needed 2 points to win, while the enemy needed 1 point.
 We were close to defeating at least one of the ships while trying to evacuate their spawn when suddenly, THE ENEMY'S THIRD SHIP REJOINED! 
Of course, with a 3v2 battle, guess who won? The enemy.
Should a ship that surrendered be able to rejoin the game? I think that was an unfair twist that upset my team's crew and really sucked the joy from the gameplay. Surrender should be a permanent option.

Even though the enemy ship rejoined, on the commendation screen, it still said "surrendered" next to the name of the one that rejoined.

[N-Sunderland]

Ships that surrender never leave the game. They're still there, though they might not have somebody piloting them (a ship surrenders automatically if the captain leaves, I think). In your case, the ship would've just been hanging around outside the fight for a long time before heading back over.

To clarify, surrendering doesn't do anything unless all of the ships on a team surrender, whereupon the match will end with a loss for that team.

[HamsterIV]

I think the ship auto surrenders after it has been completely abandoned. I have had a few captains abandon match on me and the ship was not registered as surrendered. I even won a couple by taking the helm as an engineer. As Sunderland said the surrendered ship does not leave the game. It is just an indicator that the captain doesn't want to fight the match to completion, but is polite enough not to leave mid game.

[Queso]

I'll usually surrender if we are outplayed and out-picked, but I won't leave and won't be annoyed with the other captains if they want to play on. Surrender is completely undo-able though.

[Riggatto]

Isn't there an unsurrender button in the pause menu? Whenever I've surrendered I've seen it there. I've never tried using it though. I don't see it after joining an empty ship, however.