No, removing a user from your workspace does not delete their hours.
You won’t be able to filter them out one-by-one, but the times they have tracked so far will remain accessible to you when you keep the user filter as ‘Everybody’ in the ‘Reports’ section. Here’s how you can get that user’s detailed tracking data:
1. Generate a Summary report, leaving the user filter empty (this will include everybody)
2. From the Group by selection below the chart, choose Users
3. Click on the User’s name to go to a Detailed report of them with the previously selected filters.