Can it be straightened ?

Probably.

Should it be straightened ?

Only as a practice exercise.

The frame is toast as the integrity of the joints has been compromised.

This is bad advice...

i would not worry about the forks or the frame. i would drive it like that. it looks safe to me. if the top tube and bottom tube were bent then i might be a bit worried.

I would think that the frame is still rideable. Those old steel tubes are strong as hell and the geometry is already so relaxed that it might aid from this adjustment hahaha. Sell it with a disclaimer.

John knows more about frame building than most... his advice is solid.

When we get frames like this at the shop we strip the useable parts and then cut up the frame so that no-one pulls it from the scrap bin thinking it can be built into a rideable bike.