Designing Kitchens and Bathrooms - Mortar Shower Pan Removal???

I am doing a bathroom remodel. The foundation is concrete. The existing original shower pan is a raised poured mortar bed with curb covered in 40 years worth of tile renovations. The pan is in poor condition and surrounding walls need to be re-framed due to water damage from the pan.

Question:

Do I or can I remove the existing pan by breaking it out? Was the pan poured during the original pour of the foundation and therefore a part of the foundation or poured after the foundation? Also what to do about the shower drain? The existing drain is old and rusted but it appears the only way to get it out to replace it is to break away the foundation surrounding it??? Help!!!

Not there cant see it. But Id say any pan is on top of the cement floor there. Id take it all out down to the drain . Find out what I have to do to set up a new drain to the new pan I put in or one I buy. The big box stores have the vinyl that you use to line for the new pan

I just finished a bathroom remodel where I had what sounds like the same issue. It went etremely well. looks great and
no chance for leaks

"Do I or can I remove the existing pan by breaking it out?"

Yes

"Was the pan poured during the original pour of the
foundation and therefore a part of the foundation or
poured after the foundation?"

Probably after the foundation

"Also what to do about the shower drain?"

Only you will be able to make that judgement after you
complete the tearout. The likelyhood of finding a precast
shower base that will line up with your existing drain would
be a miracle.

You should plan on using a vinyl liner as a
moisture barrier