Yes. Deleting a user removes their access from the account, but all their past time entries are kept safely in Tick’s reporting section.
Admin note: Although the deleted user’s time entries are kept, you won’t be able to find the user’s name in the “People” drop down on the reports page. This drop down shows only your active users.
You will, however, be able to look into the projects they worked on and find their time entries that way.