Microsoft recommends a minimum 80GB of disk space for System drive (C:) for a SharePoint Server 2013 (Web+App Server). doesn't that affect system availability in the future.
This is minimum requirement for the system drive. But as a practice you have to make sure none of these stored on the c drive.
- ULS logs as these will fill the drive quickly
- IIS logs
- Usage Logs.
- Index location
If you store everything on C drive then yes you environment will be in trouble.
Hardware requirements—web servers, application servers, and single server installations The values in the following table are minimum values for installations on a single server with a built-in database and for web and application servers that are running SharePoint 2013 in a multiple server farm installation. For information about the deployment types that are used in this table For all installation scenarios, you must have sufficient hard disk space for the base installation and sufficient space for diagnostics such as logging, debugging, creating memory dumps, and so on. For production use, you must also have additional free disk space for day-to-day operations. In addition, maintain two times as much free space as you have RAM for production environments.