losing constitution scores in battle; does it bring down my hp and how?

So, I run an artificer in my one campaign that just reached lv 20. Part of the lv. 20 ability (Soul of Artifice) reads:

If you’re reduced to 0 hit points but not killed out-right, you can use your reaction to end one of your artificer infusions, causing you to drop to 1 hit point instead of 0.

My artificer is using one of his infusions to replicate the amulet of health magic item which requires attunement and reads

Your Constitution score is 19 while you wear this amulet

If my character is about to be knocked down to 0 hp, and then uses his reaction to end his infusion that created the amulet, what happens?

This post is Related but I feel is still different since in this case I need to know if he would just instantly drop to 0 hp for trying to unattune to it, or if it would keep him up and still at 1 hp, just with a lowered maximum hp.