As
@Sandisw said, the tickets will disappear from your
MDE account if you do not change them before, or use them by the original dates. (since a 4 day ticket allows you to go any 4 days within 7 days of the start of the ticket, I think a 4 day ticket that starts Oct. 1st will expire and disappear from your MDE after Oct 7th.) Prior to that ticket disappearing on that date, you can change the dates yourself online and pay the price increase, if any, for the new dates. No refund is given if the new dates are less expensive. After that date, you would need to call ticketing to apply the value of the expired ticket that had disappeared from your MDE to a new ticket.
ETA: Once you know you are going to cancel your trip, you could consider changing your ticket before it expires and disappears, to dates in the future that are about the same price. That way it remains visible in your account and you can change it again online yourself for a future trip as long as you make that second change before the new expiration date. I priced a 4 day 1 park a day ticket starting Oct 1st 2021 and it came out $475.74 pretax, $506.67 after tax. If I assume that is your current ticket, if you moved that ticket to a start date of June 25th 2022, the price would go to $475.25 pretax, $506.15 after tax. You would lose 52 cents, but the ticket would remain visible in your account and you could change it yourself online later anytime before it disappears. Definitely anytime before June 25 2022, but possibly as late as July 2nd. Or you could change it to dates that are a few dollars more, pay the difference, and have that higher value to apply. (A 4 day ticket starting Sept. 29 2022 is $478.77 pretax, $509.90 after tax.)
I only mention this because it took us 4 days of getting disconnected from ticketing, sometimes after waiting a long time on hold, and then waiting over 2 hours on hold when we finally did get through. We were trying to use the credit from an expired ticket that had disappeared from our account, and that can only be done by calling ticketing. The actual change took less than 5 minutes once we got through to ticketing. Hopefully in the future wait times will be much shorter, but personally I would pay $.52 for 1 ticket, or $1.04 for 2 tickets to avoid having to call ticketing.