As egid noted, converting answers to comments deletes the answer in the process, and this is something you'll see a bit of now that you have the rep to see it. If there's ever something that has been deleted, but you feel is valuable enough to keep and voted on, just make an edit and flag it for moderator attention. They can (if they agree) delete the converted comment, and restore the answer.
A policy of not removing content that folks contribute is a great policy to cling to as long as you can. Coming back to see what you thought was something useful just removed without explanation is chilling, it doesn't make you want to participate more. That's what's great about the conversion process, it's clear to folks what happened. Stuff otherwise not converted usually has a comment attached to it explaining what the person could do if they want the post restored.
The real check in the system is just what you've pointed out, though - ordinary users that the system trusts can see this stuff, and if something is removed that shouldn't have been, it's within their means to fix it. This means even when activity has reached a level where not every answer that gets deleted receives such personalized guidance, there's still plenty of oversight.
That's not going to be for quite a while, though - not until you get on the scale of thousands of answers per day.