There are smaller blue stars that can still last a billion years or so, right? That would be at least 4 orbits around the milky way for instance. Though larger ones would obviously not last as long

This is an interesting take though, I've not seen sources explaining spiral galaxies evolving into elliptical ones even without disturbance. What would be the cause of the opposite for galaxies, when normal cloud/sphere orbits collapse into rings?

Gravity does interact over long distances over long periods of time though, is there a mechanism that acts against that compared to smaller accretion disks? What prevents an elliptical galaxy collapsing into a spiral, and how do we know that won't happen even if given a trillion years?

On the topic of spherical vs disk... do elliptical galaxies eventually collapse into spiral disks? It's a question that's always had confusion about it since spiral galaxies form by themselves but ellipticals form from collisions; if undisturbed, would spherical orbits always eventually collapse into disks (albeit perhaps taking vast amounts of time), or is it actually physically possible and statistically likely to have perfectly stable spheres that never decay?