The broken Knife

[Yrael]

I don't think he would need it as a reminder of Lyra, he has enough memories himself.

Just reaction if you broke something in public you would pick up the pieces right?

This does make sense. i would do the same.

[Halo Nerd]

The only problem Will and Lyra have is releasing a specter when they make a window. HEY! THE WORLD IS LOADED WITH SPECTERS! I see that as a huge and irritating flaw in the ending...

He keeps it indeed as a reminder and because whether it's broken or not it's still his duty as the bearer. Also of course you won't leave something with that kinda of fantastic power just lying around. If he ever has need of a dimension-splitting knife, he'll be a blacksmith away.

Of course my main thought would be, "No matter the consequence I WILL see Lyra again." and keep the knife as a reminder of the promise.

[Yrael]

The only problem Will and Lyra have is releasing a specter when they make a window. HEY! THE WORLD IS LOADED WITH SPECTERS! I see that as a huge and irritating flaw in the ending...

It's irratating, but necessary because it leaves no chance of them going back to each other.