In fact Assange's attempted gambit - of getting ironclad guarantees from Sweden that he not be extradited into the clutches of the US spook/court/torture prison complex - would, had it succeeded, have been entirely in his interests, permitting him to co-operate with investigators in Sweden without fear of 175 yrs in a US slammer, for acts which had nothing to do with sexual misconduct.
There was no "martyrdom' driving this at all. His surmise about US\UK intentions was 💯 correct.