I doubt that you would kill it with anything up to say 105 f , However being indoors can kill it. If you want something that cannot be killed by heat go with a european Olive, those things can handle higher temps than you can get in Texas.

Usually, heat dosen't kill. Sun and dry does. Zack

I have read conflicting reports on heat and Junipers, Elms bonsai etc.

Now I know the watering is always an issue regarding heat and also being placed in afternoon sun (albeit cooking roots).

This is what I am afraid of. The pots actually heating up (since the pot is practically all roots anyways) and cooking the roots. I am going to be watching my watering this summer with temps in 90s and some in 100s but can the bonsai not adapt and die from stress caused by the heat, even in the shade????

Protect the pot with i.e. white tiles leaned up against it facing the sun, or whatever will reflect the sun away from it. BTW, just a personal thing here, but it's usually better to refer to trees by their individual specie names,rather than as 'the bonsai', because I think if you see them as a collective oddity (something like 'the wife' :-) you may tend to forget they each have different characteristics and needs, and whoever reads your postings may not be sure which one you're referring to in a given sentence, or be sure how to advise you on that one tree.

I think the best question is how to protect them in the shade (while they are in the shade and not the afternoon sun).

Junipers need full sun all day, so I'm not sure why yours is in the shade.

Full sun with 90-100 in the afternoon heat would certainly be the death to a juniper bonsai.

No it wouldn't. Not if it's planted properly in a good bonsai mix, in a properly set up pot and watered appropriately. Junipers live in the SW desert under arid and very hot conditions, and if your tree is having problems it's not the 'tree's' nature causing them, but improper care.

I respect your experience Lucy but everything I have read is
morning and late afternoon sun only in the heat of the summer.

The junipers living in the SW desert are not growing in tiny pots. The roots are protected in the ground.

Well, you know, they may not be in the ground (the ? mallsai), but if they're taken care of properly (as many long time experts do) they should be o.k. I don't know where you got your info, but you might want to check a little further into things because many people grow junipers in hot climates, in all day sun, with no problems - as long as they do everything properly.

Then perhaps its the stress instead of the heat that kills them.

See ZBurkett post above. Sun and Dry kills. This is about 90-95 percent of the consensus of what is generally experienced with Junipers Lucy. We will just have to agree to disagree. Unsure of what climate you raise these in but
bonsai growers here where I live have resorted to "proper" changes, albeit larger pots, more organic mixes etc to protect our Bonsai, Trees, Junipers this summer.

Best

SA