Hi Vit Posel,
Yes, you can delete the role after 100% allocation on the role is replaced by a named resource.
Once the requisition is complete, navigate to Team - Requisition and delete the role you chose for requisition. Once the deletion is done, get back to Team Staff page and you should be able to delete the role.
But remember, if your business requires the history of requisitions done, then you shouldn't be deleting it because it will be lost forever.
Let me know how it goes.
Thanks,
Jerin