There is not any standard default htaccess file to put in place. The htaccess file is a set of instructions for your server and your site. The advice to shut down your site until you have checked everything everywhere is because if someone was able to replace/edit your htaccess file, they may have other goodies tucked in the corners of other parts of your site or its settings. You may need to work with your host to undo the damage but it is irresponsible to continue running a compromised site - and it could hurt you seriously if other people suffer malicious attacks from visiting your compromised site. Google will start showing warnings to visitors and may remove your site from their results and it can be hard to get them to let you back in to the search results.