Will macOS Big Sur remove the default Python installation for good?
No, on Apple Macs being shipped with Big Sur, Python 2 and Python 3 are both still included.
$ which python
/usr/bin/python

$ python --version
Python 2.7.16

$ which python3
/usr/bin/python3

$ python3 --version
Python 3.8.2

This is on an M1 Mac mini running macOS Version 11.0.1.