If someone said to me "Trump might change once he is sworn in", I might reply "Hope springs eternal ..."., with a touch of "Wer's glaubt wird selig", but it is not always used cynically.

It does not bring tears to my eyes.

 

The other possibility for me is "Hope is the last thing to die." Though the meaning is similar (potentially unrealistic optimism to the last), this is completely different. It has, I think, a much stronger, serious implication of vain hope. I see there is some music on Youtube with the title "Hope is the last thing to die" ( https://www.youtube.com/watch?v=RABzDAShtzI ) dedicated to the crew of the Kursk.

For me, for personal reasons, it conjures up images of the relatives of miners whose fate is unknown, when they are starting to schedule the funeral services following a mining disaster.

To my ears, all the varieties of "Hope is the last to die" sound like translations, while "Hope springs eternal" is an instantly recognisable phrase (though many might be unaware that it's a quote from Alexander Pope's poem).

However, in contexts where you feel that neither the "translationese" version nor the "poetic" version are quite right, you might just go for the simple (though not idiomatic) "Hope persists".

This is the solution I feel most appropriate in my current translation on the atrocious and perilous conditions facing refugees in the mid-19th century ... still relevant today.

Yes, or for a more rounded sentence one might say, for instance,

Hope persists against all odds

(if appropriate to the context.)