A very interesting question. I'm trading in a Note 10+ trough Samsung. This is the trade in email I received from them pertaining to the trade in condition.
Does the device turn on?
The device must start up to the home screen and function normally


Will you factory reset your device before you ship it?
You must factory reset to remove all personal data from your device.


Is your device free of cracks?
The screen and camera lenses, if applicable, must be free of cracks and function normally.


Ensure the device is not blacklisted.

They do want the associated google account removed watching their preparing phone for return but I see no mention of the S-pen. I would hate to lose my $550 trade in deal over a S-pen though.

 

I wouldn't mind keeping the S-pen for I'm not that excited about buying one. If I heard that the trade in went smoothly without the S-pen I would give it a go. You posted a valid question that I wish we had the answer to. I have until the 14th to send in my Note but I'll be sending it in with the pen sooner than that.

 

I shipped my Note 10+ back to Samsung today with the S-pen in it's silo. I guess the pen isn't that important to me for I never turned on the S-pen recognition on my S21 Ultra and tried out the pen before shipping. I might buy a pen for my office use at some point... especially if they release a full featured pen for the Ultra at some point. It's not a high priority purchase for me.

 

Samsung confirmed that they received my Note yesterday. Now they want a week or so to confirm it's condition before acknowledging my credit. I have an incredible collection of old replaced phones here because I've never traded one in. I'll feel better when my trade in is credited to my account.

 

I feel better. They accepted my trade in so I'm good. No credits mentioned. I need my credits.