In a power IC the bandgap and any cascoding is unlikely to
be significant in the end, area-wise. It's the power devices' area.
The current for a reference and housekeeping analog should
not need much device width.
Stacked MOS diodes and a resistor make a good enough shunt
regulator, a pass follower (high voltage capable) makes
a series regulator out of that. If you need fancier, then
make the thing cut over to closed loop, bandgap-referenced
when that is up. Making sure that you don't have undesirable
self-feedback going on.