Avoid or prevent native hair shock loss after FUE? Will the hair be lost forever or it will grow back?

Shock hair loss may be permanent in areas where you were genetically programmed to lose hair.

The risk of hair shock loss depends entirely on each case, the area to be transplanted and the state of the existing hairs.  Unfortunately, it can be quite unpredictable.  In general, shock loss occurs when hair is transplanted into an area that has existing hair.  If the existing hairs are weakened and thinning secondary to male of female pattern adrogenic alopecia, the procedure may "shock" these hairs and cause the hairs to shed after the transplant.  The shedding is temporary and these hairs do regrow along with the transplanted hairs.  It is best to speak with your surgeon about your concerns and the measures that can be taken before your procedure.  They will also be able to best guide you as to your potential risk.  You have mentioned the best measures to take prior to your prcoedure, starting finasteride and minoxidil.   

Use growth factors such as rogaine or propecia. Shock loss is due to the loss of normal hair whether it is from donor site or recipient area.  It can occur with both FUE and strip procedures.  Usually if it occurs it will take place in the recipient area.  
Shock loss from hair transplant can occur due to the following:
Anesthesia-  excessively long procedures taking longer than 12 hours can induce shock loss more likely.  the repeated use of lidocaine, marcaine, and perhaps most importantly epinephrine can affect nourishment of the hairTraumatic harvest-  In strip surgery, traumatic harvest can induce shock loss.  Recipient area trauma- during the incision making process the hairs are either crushed or cut and damaged during the process. 
Ways to minimize shock loss are as follows:
Improve recipient bed and donor area environment.  Make your recipient environment improved by addition of growth factors and/or PRP to help reduce incidence of shock loss to native hairs.Use of Rogaine and Propecia- can help miniaturized hair become more stable and less likely to fall out during procedure9xRobotArtas-  The latest version of the robot can make recipient sites and can determine angle of existing hair and help ensure that the angle will not damage existing hair.  Especially helpful in patients where you are transplanting hair to create densityMinimize anesthesia time and procedure time- We limit number of grafts to a safe number per session.  Extended anesthesia periods and harvest times can cause patients to have a higher chance of shock loss.  The 9x Robot harvests between 1000-1500 grafts per hour making it superior to previous additions and traditional FUE approaches.Best,
Anil Shah

Finasteride/Propecia is the best way to prevent shock loss, you should be able to start taking it pretty much right after your transplant. Hair lost via shock loss typically grows back, but if it was in it's final cycle of growth before shedding permanently due to balding/thinning, it doesn't grow back. 

Shock loss, when it happens, is usually irreversible in men. The best way to prevent this is using finasteride which your doctor should have recommended. See video