I wasn't on this cruise and have no dog in this fight, but I agree completely that if you sign up for an itinerary that was more expensive, and they switch out to a much cheaper itinerary -- that you didn't want to do anyway -- they should compensate you, at LEAST for the difference in fare.
I don't know what the pricing was before/after, but those itineraries are not comparably priced at all. This I know because we were alerted that a Celebrity "replacement" Greek Isles itinerary was sooooooo inexpensive we just added one of those in March. The web site for the 11 night Mar 25, 2024 Infinity sailing says "from $586pp" and "Was $2078." That gives you a sense of the difference. Also: We also have a sailing booked for the middle east in November on Azamara (fingers crossed it will go to most of the ports, just minus the one stop in Israel that I anticipate might be cancelled) -- which was in line with that $2000pp price when we booked, though after we booked it's gone up to insane levels like $7300pp for an INSIDE and almost $10,000pp for the least expensive balcony! Whoa!! We had wanted to maybe upgrade, but, hoooo boy, no way now.
So, yeah, Greece in October is like 75%+ less than the holy lands itinerary it replaced. I would definitely expect Celebrity to offer some serious compensation if I were the OP. It's only fair. They're earning high dollar itinerary rates and offering a low dollar replacement. Not fair at all to keep the money and run. War is horrible, but both the OP and Celebrity are impacted, so they should share the pain, not dump all the downside on the OP.
Just because a cruise contract we have no ability to negotiate says "we'll put you on a ship for N days, nothing more" -- unless it's a booze crooze we all know we're not really buying N days on some ship any random place in the world when we book a cruise. We are definitely booking for seeing specific ports, maybe missing a small percent of them -- but a sudden, completely different, much cheaper, itinerary? With no option even to cancel because you're already on board? Not fair at all, no matter what the forced legalese says. That just generates huge bad will. Silversea did this to us 10 years ago, epically bad cruise, worst cruise of the 45 cruises we've done, all things under their control they failed at, and they refused to do anything despite a revolt of most of the pax. Unknown to use beforehand, the problems had gotten so bad their CMO was (secretly-but-discovered) on board to troubleshoot. Exec. office thumbed their nose at us. We haven't sailed with them since. I'm sure it's cost them many times what it would have to make it right, but that was their call.
I hope Celebrity comes to realize treating pax badly costs them more in the end. We've got two Celebrity cruises booked, so I sure hope we don't run into the same bad treatment!
OP -- you have my sympathies.