Hey there Olivia,
Welcome to planDisney, thanks for your question and for your service!
For most
standard theme park tickets, they typically have a year or more before they expire. Therefore, if you were planning to use them but ended up not being able to go - and so your ticket is wholly unused - then you would just make a new park reservation when you're able to reschedule your visit. For standard tickets that have been used,
they usually expire 13 days after their first use.
This may potentially vary for special offer tickets, so I would suggest checking the tickets themselves or the purchase confirmation you received when you first bought them to check when they expire.
If tickets do expire before they're able to be used, then the value of those tickets are usually able to be applied toward the purchase of new tickets of equal or greater value.
Ultimately, I would suggest
reaching out to a Cast Member at the Tickets line who will be able to get the specific details of your tickets and let you know what your options will be in using them to visit the Happiest Place on Earth.
Thanks again for your question, Olivia! I hope you have a wonderful time on your next trip to the Disneyland Resort.
Have a Magical Day,
Greg