And will give way to many which thrive or evolve to thrive in hotter climates?
It's gonna take a minute (on a geological timescale) for the ecosystems to be able to reliably sustain megafauna again.
Sure, in a few million years.
Not at the pace of change we’ve chosen to accept, no.
It’s game over for a very long time
[dead]
In human time scales, the species which thrive will tend to be the adaptive generalists. Evolution takes time.