Once you've got even hundreds of satellites in non-equatorial orbits, trying to provide global coverage - their ground tracks very frequently cross each other. Even if they're all at the same orbital inclination. While those mostly won't be 90 degree crossings - the great majority will involve several km/s relative velocity. And you'd run out of (say) 5km LEO shells very quickly.
But the orbit is a minimum of about 50,000 kilometers, and the satellite is maybe a meter across. That's a very low probability of a collision per crossing.
I get that 'probably safe' or '0.001% chance of destruction per day' is not very satisfying for an investment that cost millions, but everything always comes down to odds. None of these satellites are eternal, even if they're the only thing in their orbit.
Don't know. But I'm sure that people at NASA and other such places have done that calculation. I just wanted to point out that orbital space is big, so you have to do the math to see if there's an actual problem.
Once you've got even hundreds of satellites in non-equatorial orbits, trying to provide global coverage - their ground tracks very frequently cross each other. Even if they're all at the same orbital inclination. While those mostly won't be 90 degree crossings - the great majority will involve several km/s relative velocity. And you'd run out of (say) 5km LEO shells very quickly.