If a network share is mounted (either via CLI or fstab) and network connection is subsequently lost, all file system related operations such as attempting to open a file or navigate directories in Dolphin will hang. Hanging occurs even when attempting to simply browse local files, in effect making the computer impractical to use for anything meaningful.
Yep, that'll happen. It's why manually mounting network locations via the CLI or fstab is a bad idea and why asynchronous file access systems like kio and kio-fuse were created. I would *strongly* recommend no longer manually mounting locations in the manner you're accustomed to, and instead access those locations from their URLs and let the system take care of access and mounting under the hood automatically. To create a permanent "mount" for a network location in a way that will work much better, make a link to the location using Dolphin.