Following a story that has no end is disastrous (5)
I believe the answer is:
fatal
'is disastrous' is the definition.
(similar in meaning)
'following a story that has no end' is the wordplay.
'following' becomes 'f.' (used when citing page numbers etc).
'story' becomes 'tale' (synonyms).
'that has no end' means to remove the last letter.
'tale' with its final letter taken away is 'tal'.
'f'+'a'+'tal'='FATAL'
(Other definitions for fatal that I've seen before include "Causing death, say accident" , "making one late" , "Deadly force" , "Calamitous" , "Bringing ruin" .)