Medics are protected by Geneva convention when they wear their Red Cross. This however doesn’t stop people from shooting them with the chaos of war and all. And a medic needs to defend himself/herself and any of the combatants they are trying to treat/save.

If a combat medic has to shoot back in self defense or for whatever reason shoot at enemy first, then yea the enemy should be allowed to retaliate. But shooting won’t stop a medic from providing aid. A combat medic will remain a combat medic just that they have revoked their “you cannot not shoot me “ immunity