Well, I certainly hope they do double-entry bookkeeping, off-site backups, versioning and keep old records... Plus any sane agency and companies have procedures in place so not even the boss can't mess up everything permanently with one mouse click. It'll pop up somewhere as part of the procedure. And there will be ways to reverse things. Yes, it's massively concerning that he wields that amount of power from within the government. But I think this is an extremely unlikely scenario. And Musk isn't even the type to do it this way. Plus even if... The treasury is the entity who invents the money. If Musk takes their money hostage, it'd mess up things for a while. But ultimately they could just lock him away and print new money.
I don't want to play it down. I think there will be some very bad consequences because of this. But I really don't think Musk is the main concern. He's not malicious in the same way as other politicians. He's also a memelord, likes attention, he likes to be popular and be liked by the people. I think that's amongst his motivations. And the latter makes it a bit unlikely to attack the whole population so bluntly.
And I don't think the same thing applies to other people in power. Some of them are plain evil and don't give a f... about being liked. That makes them free to commit any malicious act. And for example the president can write executive orders and mess up anything he likes. Immediately. He can bring nuclear doom upon us with a push of a button. The vice president also has quite some power. And while he seems like a complete toolbag to me, he's a very dangerous mixture of stupid?/determined? and evil. And we have some more unfortunate people in high positions.
I think I'm far more concerned with that, than with specifically Musk. But yeah, all of this is super dangerous and we can just hope for the best. Up until now a few uncomfortable things have happened. But some fears didn't manifest. I don't think it's doomsday yet.