You can disembark if you can place the models within 3" of the Raider and not within 1" of enemy models (Transport on p183). That may even be possible if you are surrounded.
You can't fire at a unit that is within 1" of an enemy unit (Choose Targets p179), so Wyches can't fire their pistols into the unit in combat with a Raider.
However, if the Wyches are in combat then they can fire with Pistols at the nearest unit (Pistol p180).
You could disembark then have the Raider fall back so you can shoot with the Wyches, but keeping the Raider in combat means you don't risk overwatch to get the Wyches in.
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From a midnight sky, there is a searing flash, a boom, a brief moment of destruction, and then it is gone.
Kabal of Lightning Strikes - Project Log
Drukhari damage output analysis