How do the other players feel about this?
If they don't have a problem with the situation then it's probably better to leave it be. So there's a brick wall mage on the team - both the team and the fixer can make use of that.
If they're not happy with the situation then you collectively need to do something about it. It could come down to playstyle differences, system familiarity, or just characters with varying karma/cash totals. Figure that out before you try to apply solutions or you may end up applying the wrong one.
Important to note that the GM is also a player and the GM deserves to have fun with the game they are running. When I've run games and stopped enjoying them it's nothing more than a chore and a job I'm not getting paid to do and that's not how I want to spend my free time.
But remember the GM always wins if he wants to and has infinite resources unlike the players. Which is why solving the issue IC doesn't work. Thor Shotting this guy does nothing but making the GM himself look like an asshole. Which is again why flat out killing a problem player is heavy handed and likely to result in OOC backlash especially if the other players had no issues. And it's really passive-aggressive to boot.
It's cute and maybe a little cathartic to suggest Thor shotting this character or have the player show up to game and be told his character was disappeared by a mega during downtime but it's also frankly just really immature and a poor way to resolve interpersonal conflict. the underlying problem will likely remain when the player makes a new character that is more powerful than the rest of the group. Or you alienate the player because they feel punished and they leave all because you couldn't say "this is affecting my ability to enjoy running this game so can we come to some agreements/house rules."
If it's really a problem for you the only long term solution is to be an adult and have a conversation with the player.
