I'm sorry I don't have the source or remember the precise details of the case,

but in this period post-Scott there was a family of runaways who were captured and ordered returned to their Southern owners (IDK, but it might have happened in Massachusetts

) by a Federal judge. To force the return required a large number of Federal troops to get the family to a ship in the face of mass protests. The entire enterprise (I do remember this quite clearly) cost $100,000!

Your tax dollars at work...
You're probably thinking of Anthony Burns in 1854.
My point, though, was that for every such case there were many more where the slave concerned was simply taken back without much trouble - ie most northerners most of the time seem to have obeyed the law. And whilst the matter never came to a test, I suspect the same would have been true (following a
Lemmon decision) in the case of slaves who tried to escape whilst accompanying their masters to Saratoga Springs or wherever.
Afaics, the Territorial issue had pretty much reached its limit. Even had Breckinridge been elected, the US Army in 1861 was only about 16,000 men - far too small to enforce a Federal slave code even in the unlikely event of Congress enacting one. Nor can I easily imagine a Congress with a Northern majority agreeing to pay for a larger army if it was likely to be employed for such a purpose. Any such attempt would have failed as Radical Reconstruction was to fail, and for the same reason - insufficient military manpower.
In short, the North had won its essential point. There was no danger of any Slave states being erected in Nebraska, the Dakotas or points west. There might just possibly be one in New Mexico, but that was only a maybe, and in any case few Northern farmers were likely to ever want to go there, so they could live with it. There would still have been occasional fights over fugitive slaves, but that alone wasn't even remotely likely to cause a war.