He cannot get himself out of the Ecuadorian embassy, but the British can get him out by:
1. Sending the Ecuadorian ambassador home to tell the president of Ecuador that Britain is considering breaking off diplomatic relations with Ecuador because that country is an outlaw nation.
2. After a week send all the other Ecuadorian diplomats home with the message that Britain will only deal with Ecuador through the Swiss embassy.
3. Wait for Julian Assange to give up because of hunger or to starve to death.
The Brits have already warned Ecuador that they will come in after him if they do not surrender him “soon”. There is precedent, they busted into the Iranian embassy in 1980 to extricate the killer of a British policewoman.