ell, My tree seems like a goner. when root pruning I got pretty drastic... I couldn't help myself. the roots were a huge mess and so i was hoping to clean them up and give this tree a chance at a nice nebari. what shocked me was when I looked at it a day or two later, the trunk had shrunk in diameter. all the leaves are drooping a bit. there is still a little life in it but after cutting maybe 75% of roots... I think i killed it. Is there anything I can do to save it? does reducing foliage help due to reducing transpiration? would a humidity tent help?

If it does loose all its leaves, does that mean its dead, or could it come back?

if it looses all its leaves, it will not be able to transport resources to the roots, so they cannot re-grow.
The trunk having shrunk in diameter indicates there is no sap flow.
Without proper roots, it probably will not regrow leaves either.

Sounds like end of story to me. But... don't just give up on it. Be patient, who knows what happens.

what species? Most species are rpotted at a time without foliage..