Bruce

From your description it seems to me that removing only as much timber as is necessary to excise the rot would be advisable. Hopefully that would allow for installing hardware that would continue the same structural functions of the timbers and buttressing foundation. My concern would be that if too much was cut, you would have to design hardware that resolved the downward and outward thrust on the rafter timbers. Not impossible but more difficult and expensive.
Re: epoxy repairs....I have done repairs and work on boats and buildings using epoxy and penetrating epoxies and am of the opinion that they have limited use for structural repairs. What the epoxy will not do is replace any significant portion of wood subjected to bending or tension. It will work for compression if it is not replacing much of the length of the member. The reason being of course that at some point in the length, compression forces are translated to bending thru deflection.
I am not in Seattle (it’s about an 1 ½ hr drive) but I may be able to help your buddy out.
If he wants to contact me I can be E-mailed at jb@cascade-crest.com

J.E.B.