Sorry about your job loss! I hope they gave you a nice package to help you transition to your next assignment.
I have never seen the word "Redundantee" and even if it is in the dictionary, I would never use it.
I don't have a good term for "people who are about to be laid off."
Perhaps you could try something like "and our soon-to-be former colleagues" or even something that tries to be cute like "our future former colleagues" but there is no way that being reminded that you are about to lose your job will make you happy, by any name.
Given that this is for a banner, I would omit the first line entirely. Just start with "Thank you... " And I agree that "We will miss you!" is shorter and to the point.
However, I don't think that "You'll always be remembered with love and warmth" is suitably ONLY if someone has died. It's a rather nice way to say "We'll miss you," I think.
Good luck with your job search.
Interested in Language