Vain and noble, otherwise impossible to sustain (9)

I believe the answer is:

nonviable

'impossible to sustain' is the definition.

'vain and noble otherwise' is the wordplay.
'and' means one lot of letters go next to another (I've seen this in other clues).
'otherwise' is an anagram indicator.
'vain' after 'noble' is 'noblevain'.
'noblevain' with letters rearranged gives 'NONVIABLE'.

I've seen this clue in The Times.

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