Definitely go back and ask about repair...
As it's a year old, the assistant will look at it as if you'd draped decaying roadkill on the cashdesk. She'll look at you sadly (poor thing, still using that old bag!) then explain nothing can be done as it's more than two seasons old.
She may - may - offer to send it away for regluing, having explained that this won't last and will be at your cost, which will be at least a hundred quid and take nearly a month. You'll have to come and collect the bag from them as no chance they could send it to you.
Alternatively she'll tell you about a repair place but you'll have to take the bag there. When you get there, the bloke will tut and tell you they always send people to him with repairs but the stuff is so crappily made it's not really repairable.
When you get the bag back, it will have a tiny tear in the pleather, which you are sure happened whilst it was being repaired but as it's been over a month since you collected it, you can't do anything.
This is why I refuse to buy designer stuff, as for the price it's just not good enough quality and retailers never offer a good repair service. The expectation is that it only needs to last two seasons, as the truly fashionable will have a new bag by then.