It's certainly a possibility. If the 9 youngest B744's are put through their third "D" check, then S/T/U could go through to 2024/5 and the 6 ER's could go to 2027/8.
At present there is no doubt that the seat mile costs of the B744 are lower than the A380 due to a lower fuel burn and lower cost of ownership (the A380's are still being leased/paid off). If the price of oil goes back up (which it will, eventually) the B744 will be even better on long range sectors in comparison to A380 seat mile costs.
When the B787 arrives in sufficient numbers to take over some of the existing A380 routes (eg DFW) then they'll struggle to find other routes that would be suitable for the A380's capacity. Thus it's possible that the A380's are disposed of before the B744.