Deleted theme via Dashboard but theme still active

I apologise in advance for this very basic question but I just want to make sure, while I’m still in the initial construction stages of my website, that I’m not setting myself up for failure.

I am using the Prestige theme (dark) and had a few teething problems installing it – first among these getting a little trigger happy with the upload of the .zip files and having both light and dark versions uploaded. Upon attempting to rectify this by deleting the light version, I deleted the dark version via Dashboard > Appearance > Themes. I didn’t delete it via FTP and just in case, I re-uploaded via FTP to wp-content/themes anyway (so now there are two Prestige themes in there as far as FTP shows me).

My concern is that I’ve somehow (though I haven’t seen the consequences of my actions yet) broken something on the backend (that I am not great with anyway) and it will come back to demolish my site later.

So, if my active theme is no longer visible in the Available Themes section of Dashboard, but it is in use and active down the left side panel…does it still exist? (I know the obvious answer is yes but I’m really really nervous of it suddenly deciding it doesn’t one day, after months and weeks of work.)

Sorry again for this potentially wildly stupid question. Any help greatly appreciated.