If you didn't delete the original group, you should maybe put everyone back into it. People can be part of more than one group, so this is a nice workaround to restore permissions, while you are figuring things out.
Many objects in the system can be shared with a group. Before moving people out, you should check templates, projects, portfolios, programs, request queues, and reports and dashboards, at the very least. While it's true that projects MAY be shared with the group, it can make sense to attribute the sharing at a portfolio level in order that the projects just inherit those permissions.
Projects are also assigned to a group (usually the group that created the project, or the group listed on the project template).
It's just not wise to delete a group without considering all of these interactions. (If you just deleted the group this week, well... it's tuesday. I recommend you head over to the Preview Sandbox, and figure out what was previously shared with the group so you can recreate those links.)