Can I repair a shower without pulling everything out?
Since I can see holes in the pan that look like they were used for installation purposes - nail holes. - An absolute certainty of failure - Tear the whole shower out.
Save yourself money in the long run.  I have replaced showers that are only 4 or 5 years old with small penetrations in the pan which caused major water damage to structural members.
If those wholes had been covered by a sealant compatible with the pan - that would be different. 

There is no way you will achieve a water tite system with the wall opened up. - Remember - thinset and grout are porous materials.  It is not the tile that makes a shower or tub water proof.  If a surface membrane had been used you might have been able to break off a couple rows of tiles and bonded another surface membrane like Kerdi  and worked your way down - doing the same to the floor.  But that still is a chancy bit of work.
Bite the bullet and start from scratch.