Would be helpful to know why it "died."
If from a soilborne disease, you are importing Big Time Problems to your Garden.

In my opinion, not worth the risk.

Thanks, that is a very good point!

Do you think that if I left it isolated and in the pot (either until it dies or until next spring when I could repot it in new soil) I would be okay?

The better question is why haven't you tossed it yet? Its a Emerald Queen Maple! lol

IMO, still not worth the risk.

Lots of growth in the last few days... maybe not a disease?
Perhaps it was just under-watered?

whaas - I haven't tossed it because it is (was) a $160 tree that I got for $0 and it will make an awesome bonsai in a few years when I can develop a canopy & nebari and reduce it to an appropriately sized bonsai pot.

It was probably some issues with the pot that killed of the top, like drought or freeze last winter. I don't think there is some disease in the soil.

That would be awesome!

Although... the top did appear to be healthy in the beginning of the season- fully budded and leaved out, and it died rather suddenly (though none of the ~10 other maples surrounding it did, and they were on the same shipment from the same grower).

jean001a - thanks for your words of caution, I will put it on the other side of the garage where there is nothing growing and post an update as to its progress after a while.

might those leaves be from the rootstock? :/

Well...

It finally gave out. Too bad, it had really nice taper/root structure below the soil - would have made a nice bonsai.

No (obvious) signs of fungus/insects in the soil/roots, but it looks like jean001a was right.