Hi,
Thank you for your query.
Yes, you can delete these options from the Status Reason.
Things to consider:
- Existing data with these values (status reasons) will be impacted and should be fixed.
- Any flows/processes/scripts/business rules/reports using these status reasons may break.
As far as I tested, out of the box processes, do not break.
I deleted all Active - Status Reasons and added a new "Sent" (in a Trial online environment).

Converted an Order to Invoice and it looks fine (it took the Sent status by default):

I also removed an option for the Paid Status Code, and when I click on Invoice Paid button, I see following:

Please note, Full is a custom option and it works fine.
In my opinion, if there was an out-of-the-box process dependent on these Status Reasons, Microsoft won't allow modifying these (like Status Code cannot be changed).
Also, here is a very nice article for your read (quite old but still applicable):
https://crmbusiness.wordpress.com/2014/07/01/crm-2013-what-happens-when-you-delete-a-status-currently-in-use/