I don't really see the moral aspect here?
I can see a lot of problem with your "company" - they shouldn't be removing people from your team without discussing it with you, and its impact on the rest of your team etc. All of those are just poor performance by the "company", so unless the actual sacking was in some way unjust (done by an individual due to personal grievance / discrimination) it's just a performance problem.
The solutions that make more sense to look at is addressing that - ie the poor management by the people who impacted your team and ignored you. Impossible to say what that would be without more information, but it might be that you talk to them / their managers about your team is now in trouble due to lack of resources and you can't now do your job due to lack of holiday etc.
However I guess you're actually relatively junior in the organisation hierarchy where that sort of discussion isn't likely (as otherwise you would have been consulted) in which case leaving may well be a reasonable option, and I'm not sure why you'd be so sure of not working anywhere else?