First decide whether your loose story lines are major or minor. What happened to a minor characters lost cat is probably not crucial. What he did with the stolen car probably is.
If the loose end is a major part of the novel you WILL need to create a major scene to deal with it. Yes it may need a rewrite, but that is better than a reader being frustrated at the end of the book.
With a minor loose end you may be able to filter the information in through your characters dialogue.
'I see Mrs Patterson's found her cat.'
The real problem writers face is finding the loose ends! This is were a good beta reader is vital. I'm not strong at micro editing, I find it difficult to spot grammatical mistakes. Now when it comes to finding plot holes and loose ends, I'm a master.
What I would advise is finding readers who are good at micro editing and good macro editors. I have yet to find someone excellent at both.
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