Hey sorry you had to wait so long for an update, we finally got together for a session, and amazingly all 9 of us were able to make it out for a session (normally I only have 5 or 6 players at a time). There were a lot of shenanigans that took place, unfortunately none with the assassin. Much to my surprise, not only did the players not plant their mines on the way out, but they actually went BACK for the untouchable amid the bombardment of the Twilight. (which in my opinion, makes him the most lovable untouchable assassin in all of history).

As for shenanigans, the arbitrator was miraculous spared volley after volley of fire from the Eldar Raiders.

The psyker roll fantastically getting 4 firebolts, only to have all of them miss his target, then when attempting to heal himself he rolled a 9 and launched himself into the air only to coming slamming down to the floor and take damage.

The guardsman missed every throw of his grenades only to have them roll directly to his enemies feet using Scatter, and then fail miserably at the damage rolls.

Needless to say we all had a few good laughs that day.

Falling damage is what terrifies my player running a psyker as well.

Unfortunately the psyker did not learn the lesson I was hoping to teach him. With a threshold of 7, and a WP of 5, using all of his power dice instead of just one to cast 'Healer ' on himself, he really was asking for trouble. I feel he's having a hard time grasping the dangers of using his powers

He'll learn when he gets a 75+ roll. They all learn.

Unfortunately the psyker did not learn the lesson I was hoping to teach him. With a threshold of 7, and a WP of 5, using all of his power dice instead of just one to cast 'Healer ' on himself, he really was asking for trouble. I feel he's having a hard time grasping the dangers of using his powers

You could amplify the consequences for using his power unchecked when he's near witnesses. Psykers are tolerated at best of times and despiced throughout the enitre Imperium. If the guy "who looks like a witch, walks like a witch and acts like a witch, but isn't a witch" starts flying around uncontrolled or gives everybody a headache when he finished his "mumbo-jumbo"-talk, chances are tolerating him will turn into torching him and despise into a deep desire to crack his skull.

I ask my players before they start playing how they feel about psykers. Most of the times, there is one in the company who doesn't really care for them. If that kind of character is put into a party with a psyker, you could have some nice interpersonal roleplaying ending with a leach for the psyker.

Unfortunately, of all the people in my group, I am the only one who hates psykers. My character was always the one to keep them in check before I started to GM.

I've been thinking about adding him back in as an NPC

Don't, trying to corral another player just because you don't like their type of character in the universe is really just going to seem antagonistic. If you want to mess with him then have enemy psykers weaken the veil around the party in a few fights and see how he likes the actual danger of causing some severe side effects.

If you put an npc there he'll likely just kill him first chance.

He actually enjoys getting perils, he's told me that he actually plans on summoning a Daemon.

Now the time to send someone in is after he summons the demon, not before. Let the be radical if they want to and teach them the error of their ways with a witch hunting squad afterwards.

From my experiences as a player, I want to keep some kind of contingency plan around. We had this exact situation take place when I played, a character summoned a Daemon, purely for his own entertainment, and left it up to the rest of the group to clean up his mess. Those of us, players, that had to burn Fate Points were not impressed. I know I certainly would have appreciated some backup or support provided by the GM at that moment. I really hate the idea of one player being able to ruin somebody else's experience 'just for the LOLs'

The summoning weapons quality in WHFRP2 has summoned daemons appear for 1d10 rounds, attack nearest target and disappear.

Alternatively, it could always offer your party a faustian bargain.

If I remember rightly, it specifically says that Pariahs cannot be targeted directly - but, for example, a telekinetically lifted boulder could be dropped on them and crushed. Therefore, I don't see a problem with using psychic powers to launch the pod, as it's not as if they are trying to launch the Pariah himself.

Pariahs aren't the same thing as Untouchables