Well let’s turn that around —
Is there any evidence that they are still alive???
No, there isn’t.
There is only evidence that their current location is unknown.
It is indeed possible that they are dead. It is indeed possible that their plane flew into Michelle Obama’s butt.
It is indeed possible, though not probable, that they flew through a rip in time and are 15 minutes in the past being menaced by Langoliers, and that they will fly their plane through the same rip and end up 10 minutes in the future, where time will catch up wit them at an airport in Bangor, Maine.
It is indeed possible that they were abducted by aliens.
It is indeed possible that they folded time and space, and instead of traveling from point A to point B, they are now lost in a dimension of Hell.
But what they are, beyond any shadow of a doubt, is lost.