Iran warns SpaceX & Starlink will be considered 'military targets'

Anything thrown up just creates a more elliptical orbit, not a higher orbit. There would have to be a second thrust at the top to bring it into an actual higher orbit.

It would still deorbit fairly quickly because the lowest part of that ellipse would still degrade quickly.

I'm prefacing this by saying my background is playing KSP and inadvertantly making my own Kessler syndrome when running out of fuel braking during a station rendezvous 😅

Yeah you're fundamentally trading energy. It depends on how the impact happens but orbital scientists think in terms of the average velocity of a collision event and their likely angle. 30⁰ head on at 7km/s is roughly normal I think?

A head on collision means that you have the full kinetic energy of both satellites to work with. Some parts get thrown up into massive orbits even up into medium earth orbit. Others deorbit due to hitting at the right angle to lose enough kinetic energy that their orbit drops.

Overall your debris ends up in a plume heading in the direction of both satellites, shaped like a flat cone. In the case of starlink they might have to deorbit the entire constellation while they still have control over them since that cone is invariably going to shotgun blast one or more satellites on the next orbital string

Those orbits will be elliptical thus they will still go trough LEO on one side of the orbit and thus lose energy. You need two boosts to create a circular orbit. With one boost only one side goes to a higher orbit height but the other side will stay at the original orbit height. The bigger problem is that they can hit other stuff when they pass trough higher orbits.

Wouldn't that end up in a highly elliptical trajectory? I don't think that would be much worse TBH.