Repair slabs set in concrete morter

Assuming the mortar has set.. if the slab has been laid on a full mortar bed and on to a proper sub base, the slab will most likely crack when trying to remove it. If it was set on small mortar dabs it may lift up without cracking.

Yes if mix is set you will need a replacement slab

The slab should be fine, but they will be a possibility you may have to replace mortar as it could have been disturbed.

Not always sometimes they can be lifted without cracking however you will need to remove the old concrete to get it back down to the right level

Its a matter of pulling it up and see . it may lift as prior mentioned if the 5 spot dab laying method was used , or if its been set in a thick wet mix , chances are it will break . slabs tend to be cheap , just relaying it is the labour cost again shouldnt take long to do . sometimes if the wet mix is too wet , after the slab is laid level it can drop as the mix dries m due to the weight of the slab pressing down essentially the mix should be just the right consistency to support the weight of the slab without dropping , or the correct procedure for sub base / ballast was not used and the ground has dropped .

Try using long wooden wedges to take the slab out, it should stop the slabs breaking