If it is as precarious as you described, then I would put place a soft catcher close beneath. The caterpillar can pupate when lying.

There is a thick bed of leaves under him. I don't think he'd be hurt if he fell.

Disruption, not hurt, is the reason.

FWIW, this happened in our butterfly garden at the rec center, and 1 of our employees removed the entire leaf with the pupae attached and carefully tied each end of the leaf to a sturdier stem. It survived, I think, because I later saw the empty chrysalis.

No pupa in the described situation.

I found him lying on the ground this morning. I think they are dying because of the cold nighttime temps. Someone said they do this in the fall as well, they feed and when it's time to pupate, they just fall on the ground and die. I'm sort of giving up on raising them to maturity here. I don't have room or time for a cage for them, and there are just too many things trying to kill them. I did find one empty chrysalis last year, and saw two newly emerged butterflies, but if that's all I get, that's all I get. It's better than nothing. I do love the flowers, so I'll keep them and hope they all don't get eaten again.

Disease or parasites MUCH more probably the cause.

Temperatures here (Central FL 9b near 9a) may not differ much from there.

I took these photos a few minutes ago.

As you see, they need no room.

I could never lock up baby cats in something that small! What do you do with the chrysalises? Surely, it's too small for them to emerge.

Anyway, nature's gonna do what nature's gonna do. I'm not going to worry about it.

The chrysales that you see are in a bag, only part of which is in clipped photo.

Yesterday, four fat cats were feeding voraciously. I'm just letting nature take its course. I'm sure more monarchs will be by to lay more eggs soon.