It's always sad when you lose a really good bird. But it seems likely that at least one of his chicks with the buff Brahma hen will turn out to be male. So he may live on yet, through his offspring.
Yes, sorry, I knew I got something wrong. The cross of a Red roo over a dark Brahma female should work for sex links, too, but it would be more difficult to sex the chicks because dark Brahma chicks are much more colorful than light Brahma chicks.
But since your chick of this cross is reddish...
The cross of RIR male over light Brahma hen works for sex links because the male is red based and the female is silver based. It won't work with buff Brahma hens because they are red based, not silver based. So your RIR x Buff Brahma chicks will have to be sexed the usual way, and that won't be...