I've found it quite common that lighting artists hit save while rendering, and when reloading the file, it starts rendering again automatically. Which isn't exactly the ideal behavior.

Is it possible to force Solaris/Houdini always to always use the HoudiniGL delegate for the viewport when loading a hip file?

This happens a lot for us too.

Does the current delegate choice even need to be saved with the hip file?

I would be interested in having that option as well. It can easily lead to a crash or hanging for long time immediately after scene is open

Yes please.