Thank you so much everyone - this is all helpful info! We do know how far it is to Seward & have a quote for $400 for taxi fare. We have four of us in our group, so it actually doesn't sound terrible. The bus is just under $300 for all of us.
I would like to verify times with Royal Caribbean - our setsail pass online says 2:30-6:30 & that's what they told me on the phone yesterday, but the last check-in time option on the app is 5-5:30, which is what is making me nervous. I'm not sure that we could drop luggage or check in before 11:30, because the earliest time is either 12:30 (on the app) or 2:30 (setsail pass).
In the past, Kenai Fjords Tours has taken care of our luggage, but they've taken it to Alaska Railroad, so I'm not sure they do that for a cruise. (We're using Kenai Fjords Tours, not Major Marine) It's a good point that they need to make it back for the train! We've done that twice without concern & as long as we can board the ship at 6, then it shouldn't be a problem.