Could be interesting, although part of me thinks you could do it more justice if you left behind the
40k setting and made you or own. That's just preference, though, and there's definitely scope for it to work as
40k.
If you're looking for inspiration, head down to Dakka Fiction and check out a story called The Geomides Affair, by Ailaros. It's rather long, but even just the first few chapters should give you a feel for Imperial beaurocracy and politics.
The only issue I'm seeing in you or synopsis is that he would be allowed to return after sanctioning; in general, psykers are either attached to Imperial Guard or Inquisitorial units for military duty, or fail the tests and are used to feed the Golden Throne. Basically, you'd need a very good reason for him to be back on his home planet, and an even better one for why he is put in charge.
That's not at all to say it can't be done. It could be as simple as him deserting from the Guard and assuming a false identity, subsequently becoming lost in the files as just another number. He could be sent back there as part of an
IG operation, and take a role in the peacekeeping, at which point he is recognised and given power in a futile attempt to appease him for the deaths.
Just some food for thought, and best of luck going forward with this. Do post what you come up with down in the Fiction forum for us to take a look at!