There have been a lot of topics on becoming a psyker, but I don't see any clear rules on what it means if you lose the trait, which is certainly possible in BC. I can see a few options, not sure which are more likely.
- You keep your psy rating and powers but you're stuck at what is almost certainly a lower power level than you'd want.
- You keep your psy rating and powers, but you can't use them. Suddenly a life in service to Tzeentch has a lot more to offer since you'll get all of that back as soon as you earn his mark and the psyker trait with it.
- Your psy rating and powers go poof. Any xp you spent on them is lost forever and if you regain the psyker trait you start from scratch.
I include 1 because I note the trait is explicitly stated as needed to buy the other things but not that it's needed to use them. I figure 2 is probably more likely but is there anything official?