"Then again, their 777's will have to placed with someone else. Which airline is big enough to takeover BA
's 777's and 744's? How is BA
's financial position?"
Theoretically they could swap 777s for A330/340s because its a more flexible aircraft family and a real alternative at least. But for the 744s there is no head-on competitor. A good part of these won´t go unless Boeing offers the 747 Advanced or Airbus a A380 "SP".
But I doubt BA
is going all-Airbus. Not even very long-term. Any major airline with the need to operate the whole range of aircraft sizes would be unwise to order from one manufacturer only. And that for several good reasons. The most important: Neither Boeing, nor Airbus have the best product in each class for each airline.
"Most of those B777's are brand new, as far as i know, they are happy with them, so if BA
were to replace the B747-400's (which i can't see happening soon) then surely one of the Long Range B777's would be a better choice."
For one BAs 777 are all older than 4 years and of the same age as the newer half of their 744s. And second the Longer Range 777 (the 300ER you´re talking about I guess) isn´t a perfect replacement for 744s if an airline has many trunk routes that fill 744s. BA
could replace 1/4 of its older 744s with them, but why? And why now? Even the oldest 744 of BA
is young enough to serve a further 10 years. A380s would certainly be more important for growth.