1) If you fail the roll, can you retreat from the Cybershark trap?
You betcha. The trap springs, becomes a Monster, and the normal rules for combat apply. Retreating is a pretty good idea, too.
2) Is a retreat (hit) classed as normal combat damage in regards to such monsters as Shadow Servant?
Good question! "Normal" combat damage occurs after a die roll. Retreat damage is simply damage dealt by the monster. This has interesting ramifications...
* Xenomorph damage effect occur any time a xenomorph deals damage, including to retreating characters. Retreating from a xenomorph is a bad idea, but ma be essential.
* Retreating from a Plasma Ghost will mess up your equipment.
* Retreating from a Shadow servant deals just one damage to each retreating character.
I hope that helps clarify what's going on with damage-triggered effects.
You're welcome. Thanks for playing the game, and thanks for asking questions. I really appreciate it.