First of all, I am not discussing anything technical here, here I am sharing my experience when I mistakenly deleted an active theme of my WordPress blog. Some times we do some changes to our theme in theme editor or by mistake also we delete the active theme in C panel. When your active theme deleted in the file manager of C panel then don’t worry, your site may be broken but your WordPress dashboard will open.
The same thing happened to me also, when I deleted a theme in Hostgator C panel, my site was broken but my WordPress dashboard was opened.
You can log in to your WordPress dashboard with your user id and password. In the dashboard go to the theme section there you can activate your required theme or you can also upload any of your favorite themes.
Remember, you can easily upload any WordPress theme in Zip format in the file manager of C panel. After extracting that file in C panel you can able to see it in WordPress dashboard. But it is very difficult to activate a theme in C panel. When your WordPress dashboard is opening then you don’t need to do that also.
Some times your dashboard may also not open in that case just wait, and after some time it will open, still, if it doesn’t open contact your hosting provider and they will solve your problem.