Secondly, as madison would then be aware you have a known flaw in your frame prior to the warranty expiring, should that flaw develop into a failure, then they would still be obliged to honour the warranty.
No they wouldn't, it states quite clearly on page 3 of Commencals 'General Warranty Conditions' that, [The Warranty is Void if - ] 'The bicycle has continued to be used while damaged.'
So obliged no, they may however use discretion when assessing your claim. If you are riding a damaged frame that is within it's warranty period, in my opinion, it's a bit daft.