Hey there Tom,
Welcome to planDisney and thanks so much for this question!
While theme park tickets are nonrefundable, and may not be resold according to the
eTicket terms and conditions page, they are able to be reassigned to someone else in your party.
Typically when you
purchase your tickets from the Disneyland Resort website, it will have you enter the names of each person using each ticket, but it's certainly understandable the plans can change! What's important to note is that this name assignment at ticket purchase is really to help you keep the tickets organized.
When you scan your ticket to enter a park on your first day, the Cast Member at the entry gate will snap a quick picture of each Guest that is assigned to their ticket for its duration. It's this photo that then officially and permanently assign the ticket to that Guest and it must be the same Guest using that ticket through its entire duration.
Therefore, if someone in your group is no longer able to go, you can just have someone else use the ticket when you all first arrive and their photo will be assigned to it - again, as long as that ticket has not yet been used.
If you need to make a few swaps or if it would be more helpful for you to have the name on the ticket changed for your own organization, then you would want to
call a Cast Member at the Tickets line who can help you make that change.
Thanks again for your question, Tom! I hope you enjoy your next trip to the Happiest Place on Earth.
Have a Magical Day,
Greg