you will have to break the pan to get it out without dropping any down the drain first thing you want is thick gloves
mop out the water first then break away at the bottom of the trap then care fully work towards the drain pulling the china away as soon as you can see down into the drain shove some paper of a roled up rubbish sak into the drain to stop bits droppping down then knock the rest of the china inwards so you dont break the collar
its not the end of the world if you do but easier if you dont
usually your going to go back with a long tailed bent pan con so if the cement has stayed in collar just slide it through if not youl have to put strong mix sand and cement around it