The last HEX is at 2357

and the last Elizabeth Line is 0007

Personally I would probably go to Paddington and then get a taxi from there. If by some miracle it wasn't too late, I would consider continuing on the Elizabeth Line to Canary Wharf and taxi / Uber the last bit. That requires you to get to Paddington by 2258. The usual maxima for taxi fares is £50 and there is a view that you should use public transport for anything more. But they have been known to pay more than this, it's just if you took the taxi the whole way you can't be 100% sure they would pay the fare. There won't be a problem getting a black cab or Uber from Paddington.