Re: Simple solution.
The UK should just end this mess by guaranteeing safe passage
They have. Straight to the nearest court to explain why he skipped bail. That said, I am in no doubt they would help him in a plane back to the Sweden he was first proclaiming to be a bastion of freedom, which he seems to confuse with a place where he can do anything he damn well pleases, screw the consequences for others.
I'm betting UK Foreign Affairs is watching all of this with amusement. There are only two parties who can end this farce, one can't do for diplomatic loss of face, the other because he'd get arrested as soon as he sticks his greasy nose out of the door. The rest of the world can just laugh at this farce, except proper asylum seekers whose last resort has been abused for avoiding the law.
However, one observation: it is quite possible that the fears about the US may turn from a frankly fanciful fiction into fact: if Assange was complicit in helping Trump (and it's clear he has), he may get sucked into the Mueller enquiry as one of the stooges of Putin - at which point he may ultimately face the extradition demands he has been pretending to exist so far.
I can't wait.