Replace rotten wall plate

[jackass]

Hello
I have a dormer built in the 70s where one of the hammer beams that the roof trusses rest on is completely rotten due to an old water damage. One of the roof trusses also seems affected.
What is the best way to address this? Is there a patch and repair method or does it have to be demolished? And is it then the entire roof that needs to be removed?
I will probably redo the roof this year and if so, I would do it at the same time.

 

[Enk Projektet]

Do you have a picture of the entire takkupa?

 

[jackass]

Do you have a picture of the entire dormer?

Unfortunately not, but here you can see a little more. If the wall is like the others in the house, it is a standing plank frame underneath.

 

[corre]

You may tear until you find healthy timber, and splice in new regular timber. Preferably over a stud or another load-bearing part.
Plywood or nail plate can also be useful, but it depends on whether there is space for it.
You splice the truss by screwing on a new healthy one on top of the existing, overlap and screw it up high. Preferably all the way up if it's a large roof or flat angle.
Unfortunately, there is no simple or less demolition-prone solution.