Wow I am amazed how far in advance a lot of you book trips. Whenever I book trips its 3 months in advance. 6 months at most.
For our WDW trips we book our rooms 499ish days out, which is the earliest a room only reservation can be booked.
The flights are booked when the airline releases the dates for booking which is about 11 months out +/-.
Our cruises we book on opening day if possible. I just booked our pre-cruise hotel for our May 2021 cruise as the dates just became available to book, though I will keep checking for a lower rate. The hotel reservation doesn't require a deposit and is cancelable until the day before arrival.
To the OP's question, we have a May 2021 Alaska cruise booked. We booked it opening day, so covid was not a declared pandemic yet, thought it was known about. We ar really torn on this, a the possibility of no vaccine by then is a significant issue for us -- we won't sail without natural or vaccine immunity. So what we've done is ALSO book the same cruise for August 2021. We will cancel one of them as we get closer to PIF for the first and more info becomes available. Quite frankly, right now we are leaning to just canceling May and keeping August as there is a better chance of a vaccine for it. That said, if there is no vaccine for the August then we move it into 2022.
Aside from the cruise itself, our other challenge will be airfare. We fly Westjet and use a companion voucher so I need to do some research on change and cancelation policies and fees before we book that.
SW