[MRM]

Send a card with a modest gift card and your regrets for not being able to attend. Give your best wishes on their union and your hopes that you can get together with them someday in the indefinite future, possibly the next time Rush plays Phoenix. I think they were just being polite by inviting you and they thought they were honoring you by inviting you. I don't think they really meant to put you on the spot. Polite regrets will be most appropriate and appreciated.