Endlessly regretting insolvency (4)
I believe the answer is:
ruin
'insolvency' is the definition.
'endlessly regretting' is the wordplay.
'endlessly' means to remove the last letter.
'regretting' becomes 'ruing' ('rue' can be a synonym of 'regret').
'ruing' with its last letter taken off is 'RUIN'.
(Other definitions for ruin that I've seen before include "Catastrophe" , "Reduce to bankruptcy" , "Destory or bankrupt" , "loss of position" , "Destroy or bankrupt" .)